diff --git a/lib/model.js b/lib/model.js
index c7b3956f6a..8a05e72dd9 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -2288,8 +2288,8 @@ Model.findOneAndUpdate = function(conditions, update, options) {
 
   if (arguments.length === 1) {
     update = conditions;
-    conditions = null;
-    options = null;
+    conditions = undefined;
+    options = undefined;
   }
 
   let fields;
@@ -2864,7 +2864,7 @@ Model.$__insertMany = function(arr, options, callback) {
   const _this = this;
   if (typeof options === 'function') {
     callback = options;
-    options = null;
+    options = undefined;
   }
 
   callback = callback || utils.noop;
diff --git a/lib/query.js b/lib/query.js
index 6333c153c6..9fab755558 100644
--- a/lib/query.js
+++ b/lib/query.js
@@ -2414,7 +2414,7 @@ Query.prototype.find = function(conditions) {
 
   this.op = 'find';
 
-  if (mquery.canMerge(conditions)) {
+  if (canMerge(conditions)) {
     this.merge(conditions);
 
     prepareDiscriminatorCriteria(this);
@@ -2436,9 +2436,14 @@ Query.prototype.find = function(conditions) {
 
 Query.prototype.merge = function(source) {
   if (!source) {
+    if (source === null) {
+      this._conditions = null;
+    }
     return this;
   }
 
+  this._conditions = this._conditions ?? {};
+
   const opts = { overwrite: true };
 
   if (source instanceof Query) {
@@ -2700,7 +2705,7 @@ Query.prototype.findOne = function(conditions, projection, options) {
     this.select(projection);
   }
 
-  if (mquery.canMerge(conditions)) {
+  if (canMerge(conditions)) {
     this.merge(conditions);
 
     prepareDiscriminatorCriteria(this);
@@ -2874,7 +2879,7 @@ Query.prototype.countDocuments = function(conditions, options) {
   this.op = 'countDocuments';
   this._validateOp();
 
-  if (mquery.canMerge(conditions)) {
+  if (canMerge(conditions)) {
     this.merge(conditions);
   }
 
@@ -2940,7 +2945,7 @@ Query.prototype.distinct = function(field, conditions, options) {
   this.op = 'distinct';
   this._validateOp();
 
-  if (mquery.canMerge(conditions)) {
+  if (canMerge(conditions)) {
     this.merge(conditions);
 
     prepareDiscriminatorCriteria(this);
@@ -3108,7 +3113,7 @@ Query.prototype.deleteOne = function deleteOne(filter, options) {
   this.op = 'deleteOne';
   this.setOptions(options);
 
-  if (mquery.canMerge(filter)) {
+  if (canMerge(filter)) {
     this.merge(filter);
 
     prepareDiscriminatorCriteria(this);
@@ -3181,7 +3186,7 @@ Query.prototype.deleteMany = function(filter, options) {
   this.setOptions(options);
   this.op = 'deleteMany';
 
-  if (mquery.canMerge(filter)) {
+  if (canMerge(filter)) {
     this.merge(filter);
 
     prepareDiscriminatorCriteria(this);
@@ -3354,7 +3359,7 @@ Query.prototype.findOneAndUpdate = function(filter, doc, options) {
       break;
   }
 
-  if (mquery.canMerge(filter)) {
+  if (canMerge(filter)) {
     this.merge(filter);
   } else if (filter != null) {
     this.error(
@@ -3524,7 +3529,7 @@ Query.prototype.findOneAndDelete = function(filter, options) {
   this._validateOp();
   this._validate();
 
-  if (mquery.canMerge(filter)) {
+  if (canMerge(filter)) {
     this.merge(filter);
   }
 
@@ -3629,7 +3634,7 @@ Query.prototype.findOneAndReplace = function(filter, replacement, options) {
   this._validateOp();
   this._validate();
 
-  if (mquery.canMerge(filter)) {
+  if (canMerge(filter)) {
     this.merge(filter);
   } else if (filter != null) {
     this.error(
@@ -4037,13 +4042,13 @@ Query.prototype.updateMany = function(conditions, doc, options, callback) {
   if (typeof options === 'function') {
     // .update(conditions, doc, callback)
     callback = options;
-    options = null;
+    options = undefined;
   } else if (typeof doc === 'function') {
     // .update(doc, callback);
     callback = doc;
     doc = conditions;
     conditions = {};
-    options = null;
+    options = undefined;
   } else if (typeof conditions === 'function') {
     // .update(callback)
     callback = conditions;
@@ -4108,13 +4113,13 @@ Query.prototype.updateOne = function(conditions, doc, options, callback) {
   if (typeof options === 'function') {
     // .update(conditions, doc, callback)
     callback = options;
-    options = null;
+    options = undefined;
   } else if (typeof doc === 'function') {
     // .update(doc, callback);
     callback = doc;
     doc = conditions;
     conditions = {};
-    options = null;
+    options = undefined;
   } else if (typeof conditions === 'function') {
     // .update(callback)
     callback = conditions;
@@ -4175,13 +4180,13 @@ Query.prototype.replaceOne = function(conditions, doc, options, callback) {
   if (typeof options === 'function') {
     // .update(conditions, doc, callback)
     callback = options;
-    options = null;
+    options = undefined;
   } else if (typeof doc === 'function') {
     // .update(doc, callback);
     callback = doc;
     doc = conditions;
     conditions = {};
-    options = null;
+    options = undefined;
   } else if (typeof conditions === 'function') {
     // .update(callback)
     callback = conditions;
@@ -5541,6 +5546,15 @@ Query.prototype.selectedExclusively = function selectedExclusively() {
 
 Query.prototype.model;
 
+/**
+ * Determine if we can merge the given value as a query filter. Override for mquery.canMerge() to allow null
+ */
+
+function canMerge(value) {
+  return value instanceof Query || utils.isObject(value) || value === null;
+
+}
+
 /*!
  * Export
  */
diff --git a/test/query.test.js b/test/query.test.js
index bca5f706cf..d8079b155f 100644
--- a/test/query.test.js
+++ b/test/query.test.js
@@ -4412,4 +4412,50 @@ describe('Query', function() {
       assert.strictEqual(doc.passwordHash, undefined);
     });
   });
+
+  it('throws an error if calling find(null), findOne(null), updateOne(null, update), etc. (gh-14948)', async function() {
+    const userSchema = new Schema({
+      name: String
+    });
+    const UserModel = db.model('User', userSchema);
+    await UserModel.deleteMany({});
+    await UserModel.updateOne({ name: 'test' }, { name: 'test' }, { upsert: true });
+
+    await assert.rejects(
+      () => UserModel.find(null),
+      /MongoServerError: Expected field filterto be of type object/
+    );
+    await assert.rejects(
+      () => UserModel.findOne(null),
+      /MongoServerError: Expected field filterto be of type object/
+    );
+    await assert.rejects(
+      () => UserModel.findOneAndUpdate(null, { name: 'test2' }),
+      /MongoInvalidArgumentError: Argument "filter" must be an object/
+    );
+    await assert.rejects(
+      () => UserModel.findOneAndReplace(null, { name: 'test2' }),
+      /MongoInvalidArgumentError: Argument "filter" must be an object/
+    );
+    await assert.rejects(
+      () => UserModel.findOneAndDelete(null),
+      /MongoInvalidArgumentError: Argument "filter" must be an object/
+    );
+    await assert.rejects(
+      () => UserModel.updateOne(null, { name: 'test2' }),
+      /MongoInvalidArgumentError: Selector must be a valid JavaScript object/
+    );
+    await assert.rejects(
+      () => UserModel.updateMany(null, { name: 'test2' }),
+      /MongoInvalidArgumentError: Selector must be a valid JavaScript object/
+    );
+    await assert.rejects(
+      () => UserModel.deleteOne(null),
+      /MongoServerError: BSON field 'delete.deletes.q' is missing but a required field/
+    );
+    await assert.rejects(
+      () => UserModel.deleteMany(null),
+      /MongoServerError: BSON field 'delete.deletes.q' is missing but a required field/
+    );
+  });
 });