When "banned.users" is not set in LCE's container-executor.cfg, submit job with user in DEFAULT_BANNED_USERS will receive unclear error message

When using LCE in a secure setup, if "banned.users" is not set in container-executor.cfg, submit job with user in DEFAULT_BANNED_USERS ("mapred", "hdfs", "bin", 0) will receive unclear error message.
for example, if we use hdfs to submit a mr job, we may see the following the yarn app overview page:

appattempt_1391353981633_0003_000002 exited with exitCode: -1000 due to: Application application_1391353981633_0003 initialization failed (exitCode=139) with output: 

while the prefer error message may look like:

appattempt_1391353981633_0003_000002 exited with exitCode: -1000 due to: Application application_1391353981633_0003 initialization failed (exitCode=139) with output: Requested user hdfs is banned 

just a minor bug and I would like to start contributing to hadoop-common with it