Checking for correct ligand code in all input files

[Ntr9999]

What I observed:
My .yml file originally had the lowercase ligand code in the setup section (a rookie error from me). However, mdpow-equilibrium is allowed to proceed when this is the case. But when it comes to -fep, it throws out an error:

Fatal error:
Did not find any molecules of type 'xxx' for coupling

xxx = your three letter ligand code (in lowercase)

But since the equilibrium files are created with the lowercase ligand code, it is then too late to change it to uppercase.

Suggestion: Throw out an error unless the ligand code is correct in ALL input files, before allowing mdpow-equilibrium to proceed, because currently it only errors at the -fep stage, at which point it is too late.