f90nml: Write bug in v0.20

I’m getting an odd bug when trying the write the following namelist:

 &a
 b%c_d_E(1)%ID = 1,
 b%c_d_E(2)%ID = 2,
 /

Code is:

    import f90nml
    data = f90nml.read('test.nml')
    with open('test_RESAVED.nml','w') as f:
        data.write(f, force=True)

Error message is:

Traceback (most recent call last):
  File "test.py", line 309, in <module>
    data.write(f, force=True)
  File "C:\Anaconda3\lib\site-packages\f90nml\namelist.py", line 232, in write
    self.write_nmlgrp(grp_name, grp_vars, nml_file)
  File "C:\Anaconda3\lib\site-packages\f90nml\namelist.py", line 253, in write_nmlgrp
    for v_str in self.var_strings(v_name, v_val, v_start=v_start):
  File "C:\Anaconda3\lib\site-packages\f90nml\namelist.py", line 302, in var_strings
    v_strs = self.var_strings(v_title, f_vals, v_start=v_start_new)
  File "C:\Anaconda3\lib\site-packages\f90nml\namelist.py", line 313, in var_strings
    i_s = v_start[::-1][len(v_idx)]
TypeError: 'NoneType' object is not subscriptable

Oddly, when I change c_d_E to c_d_e, it works fine.

I just updated to the latest release using pip. I’ve been able to read variables like this before, so something has changed.