#870 Custom export filter, conditional output, NOT operator

[Michib]

Hey Jabref-Team,

for export filters there exist AND and OR boolean operators for conditional output. Unfortunately I cannot express an important condition with these:
I want to create html code, where the publication title is a href link. It should point to the DOI, if the DOI field is present and to the url field, if no DOI is present.

Please add a NOT to the available operators.

Thanks
Michael