I am creating a JSON generator that returns the created object to be parsed in a different method. However when I am creating a field using the writeStringField method of JSON with a value of null, it throws an error of null pointer exception.

JSONGenerator gen = JSON.createGenerator(true);
gen.writeStringField('ESignature', null); <----problem here (throws a Null Pointer Exception)


Is it not possible to create a Field with null value using JSON.createGenerator?

2 Answers 2


To write null type, you should use:



gen.writeNullField(String) ;

There is a separate method given. You can not write a String by saying it null https://www.salesforce.com/us/developer/docs/apexcode/Content/apex_class_System_JsonGenerator.htm#apex_class_System_JsonGenerator


It may be the case that you want to write a string field but you are not sure that it has some value or its null.

It's always better to go with null check and then write a field.

public static String checkNullString(String sampleString) {
  String s ='';
  if(String.isBlank(sampleString)) {
    return s;
  } else {
    return sampleString;

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