Could you please add an option to ignore (treat as empty string?) variables that are set to empty or undeclared properties?

Here's an example:

I have plugin

                <groupId>io.github.git-commit-id</groupId>
                <artifactId>git-commit-id-maven-plugin</artifactId>
                <version>7.0.0</version>

Which sets properties including "${git.build.time}"

I have your plugin with

                    <vars>
                        <GIT_BUILD_TIME>${git.build.time}</GIT_BUILD_TIME>

Which is then used in the source like that

log.info("Build time: /*$GIT_BUILD_TIME$*/");

Everything works as intended

Now try to change it to

                        <GIT_BUILD_TIME></GIT_BUILD_TIME>

or

                        <GIT_BUILD_TIME>${git.build.timeUNDECLARED}</GIT_BUILD_TIME>

Both result in error:

Failed to execute goal com.igormaznitsa:jcp:7.1.0:preprocess (preprocess-sources) on project lbnet-maven-plugins-launch4j-wrp: Parameter is null -> [Help 1]

I tried < unknownVarAsFalse > true < /unknownVarAsFalse > but apparently it doesn't affect var declarations in pom, only var usage in sources.

Could you please add an option to handle that? " < allowEmptyVarDeclarations > " or something, to have them resolve to empty strings "" instead of throwing an error at buildtime?

p.s. Have I mentioned I really appreciate your work? I never understood why Java devs decided preprocessing is unnecessary.