diff --git a/src/Document/JsonDocument.st b/src/Document/JsonDocument.st
index bc550d1..a65c46b 100644
--- a/src/Document/JsonDocument.st
+++ b/src/Document/JsonDocument.st
@@ -6,7 +6,7 @@ NAMESPACE Simatic.Ax.Json
     {axcode:docs-v0:@simatic-ax/json:JsonDocument.md}
     CLASS FINAL JsonDocument IMPLEMENTS IJsonContainerElement
         VAR PUBLIC
-            buffer : ARRAY[0..999] OF CHAR;
+            buffer : REF_TO ARRAY[*] OF CHAR;
         END_VAR
         
         VAR PROTECTED
@@ -14,7 +14,6 @@ NAMESPACE Simatic.Ax.Json
             _lastElement : IJsonElementMuteable;
             _rootElement : IJsonElement;
             _lentgh : DINT;
-            _bufLowerBound : DINT;
             _bufIndex : DINT;
         END_VAR
 
@@ -42,17 +41,18 @@ NAMESPACE Simatic.Ax.Json
         /// Serializes the JSON document ino a ARRAY OF CHAR
         {axcode:docs-v0:@simatic-ax/json:JsonDocument.md}
         METHOD PUBLIC Serialize : BOOL
-            VAR_IN_OUT
-                buf : ARRAY[*] OF CHAR;
-            END_VAR
             VAR_TEMP
                 _to : IJsonElementMuteable;
+                _bufLowerBound : DINT;
             END_VAR
-
+            IF (buffer = NULL)  THEN
+                Serialize := FALSE;
+                RETURN;
+            END_IF;
             // Clear buffer (not hard before serializing)
             THIS.ClearBuffer();
 
-            _bufLowerBound := LOWER_BOUND(buf, 1);
+            _bufLowerBound := LOWER_BOUND(buffer^, 1);
             _bufIndex := _bufLowerBound;
             THIS.AddChar(c := '{');            
             
@@ -73,7 +73,11 @@ NAMESPACE Simatic.Ax.Json
             VAR_INPUT
                 c : CHAR;
             END_VAR
-            buffer[_bufIndex] := c;
+            IF (buffer = NULL)  THEN
+                AddChar := FALSE;
+                RETURN;
+            END_IF;
+            buffer^[_bufIndex] := c;
             _bufIndex := _bufIndex + 1;
             _lentgh := _lentgh + 1;
             AddChar := TRUE;
@@ -87,8 +91,12 @@ NAMESPACE Simatic.Ax.Json
             VAR_TEMP
                 i : INT;
             END_VAR
+            IF (buffer = NULL)  THEN
+                AddString := FALSE;
+                RETURN;
+            END_IF;
             FOR i := 1 TO LengthOf(s) DO
-                buffer[_bufIndex] := s[i];
+                buffer^[_bufIndex] := s[i];
                 _bufIndex := _bufIndex + 1;
                 _lentgh := _lentgh + 1;
             END_FOR;
@@ -141,11 +149,15 @@ NAMESPACE Simatic.Ax.Json
             END_VAR
             VAR_TEMP
                 i : DINT;
+                _bufLowerBound : DINT;
             END_VAR
-
+            IF (buffer = NULL)  THEN
+                RETURN;
+            END_IF;
+            _bufLowerBound := LOWER_BOUND(buffer^, 1);
             IF (hard) THEN
                 FOR i := _bufLowerBound TO _bufIndex DO
-                    buffer[i] := TO_CHAR(BYTE#16#00);
+                    buffer^[i] := TO_CHAR(BYTE#16#00);
                 END_FOR;
             END_IF;
             _bufLowerBound := 0;
diff --git a/test/Document/TestCleanResetDocument.st b/test/Document/TestCleanResetDocument.st
index 4f7e7a7..08afd12 100644
--- a/test/Document/TestCleanResetDocument.st
+++ b/test/Document/TestCleanResetDocument.st
@@ -22,6 +22,7 @@ NAMESPACE Document
             doc : JsonDocument;
             cmpBuff : ARRAY[0..399] OF CHAR;
             cmpBuffEmpty : ARRAY[0..399] OF CHAR;
+            buffer : ARRAY[0..200] OF CHAR;
             len : DINT;
         END_VAR
         
@@ -36,16 +37,18 @@ NAMESPACE Document
             o2.AddElement(o3);
             o1.AddElement(o2);
             doc.AddElement(o1);
-            doc.Serialize(doc.buffer);
+            doc.buffer := REF(buffer);
+            doc.Serialize();
 
             len := Strings.ToArray.OfCharCount(str := expString, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
             Equal(expected := LengthOf(expString), actual := doc.GetLength());
         END_METHOD
         
         {Test}
         METHOD PUBLIC TestCleanBuffer
+            doc.buffer := REF(buffer);
             // Fill Buffer
             THIS.Test_Build_nested_object_And_expect_correct_JSON();
             Equal(expected := LengthOf(expString), actual := doc.GetLength());
@@ -55,13 +58,14 @@ NAMESPACE Document
             Equal(expected := 0, actual := doc.GetLength());
 
             // compare result buffer with compare array
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
     
             // Serialize again
-            doc.Serialize(doc.buffer);
+           
+            doc.Serialize();
             len := Strings.ToArray.OfCharCount(str := expString, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
             Equal(expected := LengthOf(expString), actual := doc.GetLength());
 
@@ -79,7 +83,7 @@ NAMESPACE Document
             Equal(expected := 0, actual := doc.GetLength());
 
             // compare result buffer with compare array
-            res := CompareArray(first := doc.buffer, scnd := cmpBuffEmpty, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuffEmpty, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
     
         END_METHOD
diff --git a/test/Document/TestDoubleNestetdObject.st b/test/Document/TestDoubleNestetdObject.st
index e0714fd..66717b9 100644
--- a/test/Document/TestDoubleNestetdObject.st
+++ b/test/Document/TestDoubleNestetdObject.st
@@ -21,6 +21,7 @@ NAMESPACE Document
             res : BOOL;
             doc : JsonDocument;
             cmpBuff : ARRAY[0..399] OF CHAR;
+            buffer : ARRAY[0..200] OF CHAR;
             len : DINT;
         END_VAR
 
@@ -35,10 +36,11 @@ NAMESPACE Document
             o2.AddElement(o3);
             o1.AddElement(o2);
             doc.AddElement(o1);
-            doc.Serialize(doc.buffer);
+            doc.buffer := REF(buffer);
+            doc.Serialize();
 
             len := Strings.ToArray.OfCharCount(str := expString, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
             Equal(expected := LengthOf(expString), actual := doc.GetLength());
         END_METHOD
diff --git a/test/Document/TestJsonDocument.st b/test/Document/TestJsonDocument.st
index b53d401..e22f1c3 100644
--- a/test/Document/TestJsonDocument.st
+++ b/test/Document/TestJsonDocument.st
@@ -33,7 +33,7 @@ NAMESPACE Document
             expString : STRING;
             actString : STRING;
             result : BOOL;
-
+            buffer : ARRAY[0..200] OF CHAR;
 
 
         END_VAR
@@ -49,8 +49,9 @@ NAMESPACE Document
             
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
             
         END_METHOD
@@ -66,9 +67,10 @@ NAMESPACE Document
             
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
         END_METHOD
 
@@ -84,8 +86,9 @@ NAMESPACE Document
             
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
         END_METHOD
 
@@ -99,8 +102,9 @@ NAMESPACE Document
             
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
         END_METHOD
     
@@ -118,8 +122,9 @@ NAMESPACE Document
             
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
         END_METHOD
 
@@ -137,8 +142,9 @@ NAMESPACE Document
             
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
         END_METHOD
 
@@ -154,8 +160,9 @@ NAMESPACE Document
 
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
         END_METHOD
 
@@ -190,8 +197,8 @@ NAMESPACE Document
 
             // // Test Serialize
             // expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            // doc.Serialize(doc.buffer);
-            // result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            // doc.Serialize();
+            // result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             // Equal(expected := TRUE, actual := result);
         END_METHOD
 
@@ -216,8 +223,9 @@ NAMESPACE Document
 
             // Test Serialize
             expArrayCnt := Strings.ToArray.OfCharCount(str := expString, arr := expArray);
-            doc.Serialize(doc.buffer);
-            result := CompareArray(first := doc.buffer, scnd := expArray, count := TO_INT(expArrayCnt));
+            doc.buffer := REF(buffer);
+            doc.Serialize();
+            result := CompareArray(first := buffer, scnd := expArray, count := TO_INT(expArrayCnt));
             Equal(expected := TRUE, actual := result);
     
         END_METHOD
diff --git a/test/Document/TestJsonLongDocument.st b/test/Document/TestJsonLongDocument.st
index 7d9f3c4..02c1abd 100644
--- a/test/Document/TestJsonLongDocument.st
+++ b/test/Document/TestJsonLongDocument.st
@@ -11,13 +11,14 @@ NAMESPACE Document
             e2 : JsonLInt := (Key := 'elem2', Value := 1);
             e3 : JsonDInt := (Key := 'elem3', Value := 2);
             doc :JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
         
         METHOD PUBLIC MyMethod
             doc.AddElement(e1);
             doc.AddElement(e2);
             doc.AddElement(e3);
-            doc.Serialize(doc.buffer); //--> {elem1: 0, elem2: 1, elem3: 2}\n
+            doc.Serialize(); //--> {elem1: 0, elem2: 1, elem3: 2}\n
             // nice to have --> doc.Deserialize('{elem1: 99, elem2: 100, elem3: 111}\n')
         END_METHOD
 
diff --git a/test/Document/TestResetNestedDocument.st b/test/Document/TestResetNestedDocument.st
index b664826..365bdf3 100644
--- a/test/Document/TestResetNestedDocument.st
+++ b/test/Document/TestResetNestedDocument.st
@@ -17,51 +17,58 @@ NAMESPACE Document
             myDint : JsonDInt := (Value := DINT#12345678, Key := 'myDint');
             myString : JsonString := (Value := 'this is my string', Key := 'myString');
             myObject : JsonObject := (Key := 'myObject');
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
         METHOD PUBLIC Serialize_BOOLEAN
+            doc.buffer := REF(buffer);
+
             doc.AddElement(myBoolean);
-            doc.Serialize(doc.buffer);
+            doc.Serialize();
             
-            str := Arrays.ToString(doc.buffer, 0, 18);
+            str := Arrays.ToString(buffer, 0, 18);
             Equal(expected := '{"myBoolean": true}', actual := str);
         END_METHOD
 
         {Test}
         METHOD PUBLIC Serialize_INT
+            doc.buffer := REF(buffer);
             doc.AddElement(myInt);
-            doc.Serialize(doc.buffer);
+            doc.Serialize();
             
-            str := Arrays.ToString(doc.buffer, 0, 14);
+            str := Arrays.ToString(buffer, 0, 14);
             Equal(expected := '{"myInt": 1234}', actual := str);
         END_METHOD
 
         {Test}
         METHOD PUBLIC Serialize_DINT
+            doc.buffer := REF(buffer);
             doc.AddElement(myDint);
-            doc.Serialize(doc.buffer);
+            doc.Serialize();
             
-            str := Arrays.ToString(doc.buffer, 0, 19);
+            str := Arrays.ToString(buffer, 0, 19);
             Equal(expected := '{"myDint": 12345678}', actual := str);
         END_METHOD
         
         {Test}
         METHOD PUBLIC Serialize_STRING
+            doc.buffer := REF(buffer);
             doc.AddElement(myString);
-            doc.Serialize(doc.buffer);
+            doc.Serialize();
             
-            str := Arrays.ToString(doc.buffer, 0, 32);
+            str := Arrays.ToString(buffer, 0, 32);
             Equal(expected := '{"myString": "this is my string"}', actual := str);
         END_METHOD
 
         {Test}
         METHOD PUBLIC Serialize_INT_DINT
+            doc.buffer := REF(buffer);
             doc.AddElement(myInt);
             doc.AddElement(myDint);
-            doc.Serialize(doc.buffer);
+            doc.Serialize();
             
-            str := Arrays.ToString(doc.buffer, 0, 34);
+            str := Arrays.ToString(buffer, 0, 34);
             Equal(expected := '{"myInt": 1234, "myDint": 12345678}', actual := str);
         END_METHOD
 
@@ -73,9 +80,10 @@ NAMESPACE Document
             doc.AddElement(myBoolean);
             doc.AddElement(myObject);
             
-            doc.Serialize(doc.buffer);
+            doc.buffer := REF(buffer);
+            doc.Serialize();
             
-            str := Arrays.ToString(doc.buffer, 0, 67);
+            str := Arrays.ToString(buffer, 0, 67);
             Equal(expected := '{"myBoolean": true, "myObject": {"myInt": 1234, "myDint": 12345678}}', actual := str);
 
 
@@ -89,8 +97,8 @@ NAMESPACE Document
             doc.AddElement(myBoolean);
             doc.AddElement(myObject);
 
-            doc.Serialize(doc.buffer);
-            str := Arrays.ToString(doc.buffer, 0, 67);
+            doc.Serialize();
+            str := Arrays.ToString(buffer, 0, 67);
             Equal(expected := '{"myBoolean": true, "myObject": {"myInt": 1234, "myDint": 12345678}}', actual := str);
 
         END_METHOD
diff --git a/test/Numbers/ItemTestInt.st b/test/Numbers/ItemTestInt.st
index 2bd4a84..054a932 100644
--- a/test/Numbers/ItemTestInt.st
+++ b/test/Numbers/ItemTestInt.st
@@ -13,6 +13,7 @@ NAMESPACE Simatic.Ax.Json
             s_test_minus_999 : STRING := '"second_key": -999';
             cmpBuff : ARRAY[0..20] OF CHAR;
             doc : JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -35,10 +36,12 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
+            doc.buffer := REF(buffer);
+
             e.Serialize(REF(doc));
 
             len := Strings.ToArray.OfCharCount(str := s_test_999, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
@@ -49,10 +52,10 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
-            
+            doc.buffer := REF(buffer);
             e2.Serialize(REF(doc));
             len := Strings.ToArray.OfCharCount(str := s_test_minus_999, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
diff --git a/test/Numbers/ItemTestSint.st b/test/Numbers/ItemTestSint.st
index c48cdef..ae55830 100644
--- a/test/Numbers/ItemTestSint.st
+++ b/test/Numbers/ItemTestSint.st
@@ -13,6 +13,7 @@ NAMESPACE Simatic.Ax.Json
             s_test_min : STRING := '"second_key": -128';
             cmpBuff : ARRAY[0..20] OF CHAR;
             doc : JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -35,10 +36,11 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
+            doc.buffer := REF(buffer);
             e.Serialize(REF(doc));
 
             len := Strings.ToArray.OfCharCount(str := s_test_max, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
@@ -49,10 +51,10 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
-            
+            doc.buffer := REF(buffer);
             e2.Serialize(REF(doc));
             len := Strings.ToArray.OfCharCount(str := s_test_min, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
diff --git a/test/Numbers/ItemTestUInt.st b/test/Numbers/ItemTestUInt.st
index 5d753fb..9e5e0ca 100644
--- a/test/Numbers/ItemTestUInt.st
+++ b/test/Numbers/ItemTestUInt.st
@@ -13,6 +13,7 @@ NAMESPACE Simatic.Ax.Json
             s_test_max : STRING := '"second_key": 65535';
             cmpBuff : ARRAY[0..20] OF CHAR;
             doc : JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -35,10 +36,11 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
+            doc.buffer := REF(buffer);
             e.Serialize(REF(doc));
 
             len := Strings.ToArray.OfCharCount(str := s_test_min, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
@@ -49,10 +51,10 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
-            
+            doc.buffer := REF(buffer);
             e2.Serialize(REF(doc));
             len := Strings.ToArray.OfCharCount(str := s_test_max, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
diff --git a/test/Numbers/ItemTestUSint.st b/test/Numbers/ItemTestUSint.st
index 159acd3..6fa7cdb 100644
--- a/test/Numbers/ItemTestUSint.st
+++ b/test/Numbers/ItemTestUSint.st
@@ -13,6 +13,7 @@ NAMESPACE Simatic.Ax.Json
             s_test_minus_min : STRING := '"second_key": 0';
             cmpBuff : ARRAY[0..20] OF CHAR;
             doc : JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -35,10 +36,11 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
+            doc.buffer := REF(buffer);
             e.Serialize(REF(doc));
 
             len := Strings.ToArray.OfCharCount(str := s_test_max, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
@@ -49,10 +51,10 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
-            
+            doc.buffer := REF(buffer);
             e2.Serialize(REF(doc));
             len := Strings.ToArray.OfCharCount(str := s_test_minus_min, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
diff --git a/test/Numbers/TestJsonBoolean.st b/test/Numbers/TestJsonBoolean.st
index ac7ce31..9cec56c 100644
--- a/test/Numbers/TestJsonBoolean.st
+++ b/test/Numbers/TestJsonBoolean.st
@@ -12,6 +12,7 @@ NAMESPACE Simatic.Ax.Json
             expString, actString : STRING;
             cmpBuff : ARRAY[0..20] OF CHAR;
             doc : JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -20,11 +21,12 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
+            doc.buffer := REF(buffer);
             e.Serialize(REF(doc));
 
             expString := '"test": true';
             len := Strings.ToArray.OfCharCount(str := expString, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
@@ -35,11 +37,11 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
-            
+            doc.buffer := REF(buffer);
             e2.Serialize(REF(doc));
             expString := '"second_key": false';
             len := Strings.ToArray.OfCharCount(str := expString, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD
diff --git a/test/Object/TestJsonObject.st b/test/Object/TestJsonObject.st
index 6fb04d7..5b8d599 100644
--- a/test/Object/TestJsonObject.st
+++ b/test/Object/TestJsonObject.st
@@ -14,6 +14,7 @@ NAMESPACE Simatic.Ax.Json
             doc : JsonDocument;
             cmpBuff : ARRAY[0..399] OF CHAR;
             len : DINT;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -74,11 +75,11 @@ NAMESPACE Simatic.Ax.Json
             THIS.Test_Object_with_three_elements();
             _expStr := '"Name": {"test": 999, "second_key": -999, "3rd": 1}';
 
-            
+            doc.buffer := REF(buffer);
             o.Serialize(REF(doc));
 
             len := Strings.ToArray.OfCharCount(str := _expStr, arr := cmpBuff);
-            _res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            _res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := _res);
         END_METHOD
 
diff --git a/test/String/TestJsonString.st b/test/String/TestJsonString.st
index 05ebdc3..015e15f 100644
--- a/test/String/TestJsonString.st
+++ b/test/String/TestJsonString.st
@@ -12,6 +12,7 @@ NAMESPACE Simatic.Ax.Json
             expString, actString : STRING;
             cmpBuff : ARRAY[0..20] OF CHAR;
             doc : JsonDocument;
+            buffer : ARRAY[0..200] OF CHAR;
         END_VAR
 
         {Test}
@@ -20,11 +21,12 @@ NAMESPACE Simatic.Ax.Json
                 len : DINT;
                 res : BOOL;
             END_VAR
+            doc.buffer := REF(buffer);
             e.Serialize(REF(doc));
 
             expString := '"test": "my#1234,,,,"';
             len := Strings.ToArray.OfCharCount(str := expString, arr := cmpBuff);
-            res := CompareArray(first := doc.buffer, scnd := cmpBuff, count := TO_INT(len));
+            res := CompareArray(first := buffer, scnd := cmpBuff, count := TO_INT(len));
             Equal(expected := TRUE, actual := res);
 
         END_METHOD