Input validation checks fail on TSV when object null()

[jfy133]

Check Documentation

I have checked the following places for your error:

• nf-core website: troubleshooting
• nf-core/eager pipeline documentation
  - nf-core/eager FAQ/troubleshooting can be found here

Description of the bug

A user forgot to add NA in the their BAM column, and the TSV file also didn't use quote wrapping. The current input validation only checks ifEmpty() which doesn't seem to work on null() objects.

Steps to reproduce

Make input TSV with empty cell instead of NA.

Should result in

Cannot invoke method isEmpty() on null object

error.

Expected behaviour

The validation check should also die when null() object, and give informative error message.

Additional context

https://stackoverflow.com/questions/25039270/how-to-groovy-ify-a-null-check