How to find non-parametrised bonds?

[iGulitch]

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Hello!

The code :

mol = mbuild.load('<name>.pdb')
ff = foyer.Forcefield(name = 'oplsaa')
mol_ff = ff.apply(mol)

gives :

Exception: Parameters have not been assigned to all bonds. Total system bonds: <N>, Parametrized bonds: <M>

How can I find between which atoms there are bonds that Foyer can't parametrise?

Thanks!