Make material default libraries None-able

[MicahGale]

Is your feature request related to a problem? Please describe.

I was trying to delete the default library for a material (e.g., remove the nlib=...).

I tried:

mat.default_libraries[montepy.NEUTRON] = None # I forgot what the string version of the particle should be.

Instead I got:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[9], line 1
----> 1 mat.default_libraries[montepy.Particle.NEUTRON] = None

File ~/miniforge3/envs/openmc/lib/python3.12/site-packages/montepy/data_inputs/material.py:63, in _DefaultLibraries.__setitem__(self, key, value)
     62 def __setitem__(self, key, value):
---> 63     key = self._validate_key(key)
     64     if not isinstance(value, (Library, str)):
     65         raise TypeError("")

File ~/miniforge3/envs/openmc/lib/python3.12/site-packages/montepy/data_inputs/material.py:96, in _DefaultLibraries._validate_key(key)
     94     raise TypeError("")
     95 if not isinstance(key, LibraryType):
---> 96     key = LibraryType(key.upper())
     97 return key

File ~/miniforge3/envs/openmc/lib/python3.12/enum.py:751, in EnumType.__call__(cls, value, names, module, qualname, type, start, boundary, *values)
    749     if names is not _not_given:
    750         value = (value, names) + values
--> 751     return cls.__new__(cls, value)
    752 # otherwise, functional API: we're creating a new Enum type
    753 if names is _not_given and type is None:
    754     # no body? no data-type? possibly wrong usage

File ~/miniforge3/envs/openmc/lib/python3.12/enum.py:1170, in Enum.__new__(cls, value)
   1168 ve_exc = ValueError("%r is not a valid %s" % (value, cls.__qualname__))
   1169 if result is None and exc is None:
-> 1170     raise ve_exc
   1171 elif exc is None:
   1172     exc = TypeError(
   1173             'error in %s._missing_: returned %r instead of None or a valid member'
   1174             % (cls.__name__, result)
   1175             )

ValueError: 'N' is not a valid LibraryType

Which is a bug. I remember that I should use "nlib", and instead got.

----> 1 mat.default_libraries["nlib"] = None

File ~/miniforge3/envs/openmc/lib/python3.12/site-packages/montepy/data_inputs/material.py:65, in _DefaultLibraries.__setitem__(self, key, value)
     63 key = self._validate_key(key)
     64 if not isinstance(value, (Library, str)):
---> 65     raise TypeError("")
     66 if isinstance(value, str):
     67     value = Library(value)

TypeError:

Describe the solution you'd like

The only way that currently works is to do:

del mat.default_libraries["nlib"]

Additional context

This is a bug and a feature request. A few tasks I see:

1. Fix the bug where you can't pass a montepy.Particle
2. Actually fill out the TypeError message
3. Allow None values.

[MicahGale]

Actually I seem to remember that Particle was not allowed due to the ambiguity of photons. I might reverse this decision.