anchor.diff:  +
   [source,Painless]
   ----
  -long inputDatetime = ctx['_source']['input_datetime']; <1>
  +long inputDateTime = ctx['_source']['input_datetime']; <1>
   Instant instant = Instant.ofEpochMilli(inputDateTime);
   ZonedDateTime zdt = ZonedDateTime.ofInstant(instant, ZoneId.of('Z'));
   ----
  
positive.code: <1> When a query's results span multiple indexes, some indexes may not
  contain a specific field. Use the `containsKey` method call on the `doc` input
  to ensure a field exists as part of the index for the current document.
  <2> Some field's within a document may have no values. Use the `size` method
  call on a field within the `doc` input to ensure that field has at least one
  value for the current document.
  
negative.code: +
  [source,Painless]
  ----
  long inputDateTime = params['input_datetime'];
  Instant instant = Instant.ofEpochMilli(inputDateTime);
  ZonedDateTime zdt = ZonedDateTime.ofInstant(instant, ZoneId.of('Z'));
  ----
  