No processed css and js files in target directory using wro4j-maven-plugin

[LisaPug]

I tried to implement the wro4j-maven-plugin to a testproject but do not get any output in my target directory after running maven "clean install". I played around with different versions of the plugin, for example 1.7.5 (where the build is successful, but without an output of processed css files) and 1.8.0 where the build fails.
The plugin in pom.xml looks like this:

Dependencies in pom.xml:

My wro.xml:

My wro.properties:
preProcessors=cssMin

My console output:

The error message says:
Failed to execute goal ro.isdc.wro4j:wro4j-maven-plugin:1.8.0:run (default) on project wroNeu: Exception occured while processing: ro.isdc.wro.WroRuntimeException: Exception while merging resources: No valid resource '/css/style.css' found inside any of contextFolders: [C:\Users\lkuhlmann\workspaceNeu\wroNeu\src\main\frontend], class: ro.isdc.wro.WroRuntimeException,caused by: java.io.IOException: C:\Users\lkuhlmann\workspaceNeu\wroNeu\src\main\frontend\css\style.css (Das System kann den angegebenen Pfad nicht finden) -> [Help 1]

My project structure:

If I try it with version 1.7.5 the console output when running mvn clean install is as follows:

I work on a Windows PC.
Does anybody know what I am doing wrong?

[alexo]

@LisaPug have you found the cause of the problem?
Btw, the project has moved to https://github.com/wro4j/wro4j/

[LisaPug]

Yes, thank you for asking. I changed the path to my css and js files in wro.xml this way:

Now it works :)

[alexo]

It is recommended to use servlet context relative path. This way it will work on any environment.
Your approach works, but it uses absolute path which can differ on different machine.