Should default values for LJ parameters assumed when creating new AtomType?

[rsdefever]

from gmso.core.atom_type import AtomType
atom_type = AtomType(name="cc", mass=12.010, expression="4*epsilon*((sigma/r)**12 - (sigma/r)**6)")
print(atom_type.parameters)

Gives:

{'sigma': unyt_quantity(0.3, 'nm'), 'epsilon': unyt_quantity(0.3, 'kJ')}

This seems dangerous to me. Can we make them zero or nan or something? Thoughts?