code: public void setCustomFieldValue(String fieldNameOrApiId, String value) {
          CustomField f = new CustomField();
          f.setName(fieldNameOrApiId);
          f.setValue(value);
          customFields.add(f);
      }
docs: Adds the value to fill in for a custom field with the given field name.
  
  @param fieldNameOrApiId String name (or "Field Label") of the custom field
  to be filled in. The "api_id" can also be used instead of the name.
  @param value String value