code: protected void appendFieldStart(StringBuilder buffer, String fieldName) {
          if (useFieldNames && fieldName != null) {
              buffer.append(fieldName);
              buffer.append(fieldNameValueSeparator);
          }
      }
docs: <p>Append to the <code>toString</code> the field start.</p>
  
  @param buffer    the <code>StringBuilder</code> to populate
  @param fieldName the field name