[FEATURE] Better error message when running quantms with no input

[fabianegli]

Description of feature

When running the simplest nextflow command with quantms, the error is quite cryptic. I believe it should point to some resources and give a useful help message in the terminal.

Example run:

% nextflow run bigbio/quantms 

 N E X T F L O W   ~  version 25.04.7

Pulling bigbio/quantms ...
 downloaded from https://github.com/bigbio/quantms.git
Launching `https://github.com/bigbio/quantms` [reverent_volhard] DSL2 - revision: e516ddca04 [master]

Downloading plugin [email protected]
ERROR ~ Argument of `file` function cannot be null

 -- Check script '.nextflow/assets/bigbio/quantms/workflows/quantms.nf' at line: 45 or see '.nextflow.log' file for more details