added option to skip template if column value is NULL

[akademic]

Suggest option autonull

filters:
  my_table:
    columns:
      last_name:
        value: "{{- randAlphaNum 20 | nospace -}}"
        autonull: true

if autonull is true than if column has NULL value do not transform it with templates

Pitfalls: if NULL value has whitespace before it will not be null, but it will be correct quoted string. But it is parser issue.

[akademic]

not actual any more