Description of problem:
With zanata-cli installed on Fedora today using `sudo yum install zanata-client`, trying to push a single xliff file caused a NullPointerException in PushCommand.validateValidation(). Repeating the same command with ` --validate CONTENT` appended does not generate a NullPointerException.

Version-Release number of selected component (if applicable):
Client version is unknown since the --version command generates no output.


How reproducible:
Easy, always

Steps to Reproduce:
1. sudo yum install zanata-cli
2. create a project config for an xliff project
3. run `zanata-cli -e push -s src -t trans`
4. run `zanata-cli -e push -s src -t trans --validate CONTENT`

Actual results:
3. NullPointerException is reported.
4. No exception is reported.


Expected results:
3 & 4. No exception is reported.