plugin execution fails when no xspec tests are found

[jpraet]

Before (2.0.0-RC3):

[INFO] --- xspec-maven-plugin:2.0.0-RC3:run-xspec (default-run-xspec) @ EPVDocumentsFW ---
[INFO] Found 0 XSpecs...

Now (2.0.0):

[ERROR] Failed to execute goal io.xspec.maven:xspec-maven-plugin:2.0.0:run-xspec (default-run-xspec) on project EPVDocumentsFW: Execution default-run-xspec of goal io.xspec.maven:xspec-maven-plugin:2.0.0:run-xspec failed: no execution has been done. processedFiles is null -> [Help 1]