Java param lib: Execution crashes when env var _SQUASH_TF_TESTCASE_PARAM_FILES is not present

When trying to run a JUnit project with the java param library and the _SQUASH_TF_TESTCASE_PARAM_FILES environment variable (which normally contains the name of the .ini) is not present, then the test crashes with NoClassDefFound / NPE / ExceptionInInitializerError .

Likewise if the variable is set but the file cannot be found, we get NPEs everywhere.

This was not seen in the QA analysis because this variable is injected by default by the orchestrator, we encounter this problem mainly when running a test locally.

Seen with 1.0.0 of lib.