When supplying a wrong user_main like this
The Nemo client tries to launch the application, which fails immediately since the class is not found. We can avoid this by rejecting applications that have invalid configuration.
You can reproduce this bug with the following command:
./bin/run_beam.sh -job_id mr_default -executor_json `pwd`/examples/resources/beam_test_executor_resources.json -optimization_policy org.apache.nemo.compiler.optimizer.policy.DefaultPolicy -user_main XXX -user_args "`pwd`/examples/resources/test_input_wordcount `pwd`/examples/resources/test_output_wordcount"