Removing content when not replace

[ghost]

Hello,

When I use this action on a file that has the same pattern in a parameter that I don't want to replace - and therefore not sending it, the task will replace it with empty string.

for example:

File a.txt:

a=#{param}#
b=#{nana}#

task:

      - name: Replace tokens
        uses: cschleiden/[email protected]
        with:
          files: '["a.txt"]'
        env:
          param: lala

at the end the file will be:

a=lala
b=

but I would like it to be:

a=lala
b=#{nana}#

I think it should replace the parameter only if I gave it.