Parameter “checksum” permit to retrieve the CRC checksum (a numeric code) of the returning value. Empty String ('') return 0 but it's not the case for Null Value.

NOTE: By default the resulting content will be parsed (all <#..> tags will be evaluated) before to apply this filter. You can control this behavior throught the parameter AnalyzeTagParams

  <#TestVar setValue="hello">
  <#TestVar checksum="1">
  

will output

  68623423