Pass unit tests on Python 3.7

[bobleesj]

The PR fixes two 2 failed test cases using the diffpy-cmi Conda environment

When op._value = None, getValue() returns TypeError instead of ValueError.

Ideally, we use ValueError as it was originally; we shall backburner this after we do cookiecutting. I will leave an issue.

Local test:

All 110 tests pass.

imac@imacs-iMac diffpy.srfit % python -m diffpy.srfit.tests.run
WARNING:diffpy.srfit.tests:No module named 'sas', SaS tests skipped.
WARNING:diffpy.srfit.tests:Cannot import diffpy.structure, Structure tests skipped.
WARNING:diffpy.srfit.tests:Cannot import pyobjcryst, pyobjcryst tests skipped.
WARNING:diffpy.srfit.tests:Cannot import diffpy.srreal, PDF tests skipped.
......ssss...........sss..................sssssssssss....ssssss...........................ssssss..............
----------------------------------------------------------------------
Ran 110 tests in 0.184s

Conda enviornment (used conda install diffpy-cmi)

# Name                    Version                   Build  Channel
ca-certificates           2024.7.4             h8857fd0_0    conda-forge
diffpy-srfit              3.0.0.post10             pypi_0    pypi
libcxx                    18.1.8               heced48a_4    conda-forge
libffi                    3.4.2                h0d85af4_5    conda-forge
libsqlite                 3.46.0               h1b8f9f3_0    conda-forge
libzlib                   1.3.1                h87427d6_1    conda-forge
ncurses                   6.5                  h5846eda_0    conda-forge
numpy                     1.21.6                   pypi_0    pypi
openssl                   3.3.1                h87427d6_2    conda-forge
pip                       24.0               pyhd8ed1ab_0    conda-forge
python                    3.7.12          hf3644f1_100_cpython    conda-forge
readline                  8.2                  h9e318b2_1    conda-forge
setuptools                69.0.3             pyhd8ed1ab_0    conda-forge
sqlite                    3.46.0               h28673e1_0    conda-forge
tk                        8.6.13               h1abcd95_1    conda-forge
wheel                     0.42.0             pyhd8ed1ab_0    conda-forge
xz                        5.2.6                h775f41a_0    conda-forge

In the next PRs, I will submit flake8 autolinted for few files at a time.

[sbillinge]

@bobleesj it wasn't clear to me if you want this merged or not. Happy to merge it.

[bobleesj]

@sbillinge Yes please merge it.