[explorer] fix: not render button when payload is empty

Author: AnthonyLaw

__tests__/components/fileds/MessageField.spec.js

@@ -106,5 +106,12 @@ describe('MessageField component', () => {
 				payload: '48656C6F2066726F6D2073796D626F6C20736E6170'
 			});
 		});
+
+		it('does not render convert message button when plain message payload is empty', () => {
+			assertConvertFormatButtonNotRender({
+				type: 0,
+				payload: ''
+			});
+		});
 	});
-});
+});

src/components/fields/MessageField.vue

@@ -78,7 +78,7 @@ export default {
 			return this.isViewAsUTF8 ? `View as default` : `View as utf-8`;
 		},
 		isHexString () {
-			return Convert.isHexString(this.value.payload);
+			return this.value.payload && Convert.isHexString(this.value.payload);
 		}
 	},
 	methods: {