This fix is for the following issue taken from the docstring example (with a few mods):

import flopy
ml = flopy.mfusg.MfUsg()
node_prop = [
    [1, 1, 0, 10.0, -110.0, 1.57, 0, 0],
    [2, 1, 0, 10.0, -130.0, 1.57, 0, 0],
]
cln_gwc = [
    [1, 1, 50, 50, 0, 0, 10.0, 1.0, 0],
    [2, 2, 50, 50, 0, 0, 10.0, 1.0, 0],
]
cln_circ = [[1, 0.5, 3.23e10]]
cln = flopy.mfusg.MfUsgCln(ml, ncln=1, iclnnds=-1, nndcln=2,
    nclngwc=2, node_prop=node_prop, cln_gwc=cln_gwc, cln_circ=cln_circ)

Traceback (most recent call last):
File "", line 12, in
cln = flopy.mfusg.MfUsgCln(ml, ncln=1, iclnnds=-1, nndcln=2,
nclngwc=2, node_prop=node_prop, cln_gwc=cln_gwc, cln_circ=cln_circ)
File "/home/mtoews/src/FloPy/flopy/flopy/mfusg/mfusgcln.py", line 235, in init
setattr(self, f"i{attr}", int(unitnumber[idx + 1]))

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.5%. Comparing base (556c088) to head (71709b4).
⚠️ Report is 42 commits behind head on develop.

@@             Coverage Diff             @@
##           develop    #2595      +/-   ##
===========================================
+ Coverage     55.5%    72.5%   +16.9%     
===========================================
  Files          644      667      +23     
  Lines       124135   128669    +4534     
===========================================
+ Hits         68947    93309   +24362     
+ Misses       55188    35360   -19828