UnboundLocalError: local variable 'fig' referenced before assignment

[xushanthu-2014]

The error happens when I ran the code:

    import matplotlib.pyplot as plt
    fig = plt.figure(figsize=(25, 7))
    ax1 = fig.add_subplot(111, projection='polar')
    ax2 = fig.add_subplot(121, projection='polar')
    
    # plot BRDF and phase function
    plot1 = SRF.polarplot(inc = list(np.linspace(0,85,5)), multip = 1.5, legpos = (0.,0.5), polarax=ax2,
                         label='Surface scattering phase function', legend=True)
    plot2 = V.polarplot(inc = list(np.linspace(0,120,5)) ,multip = 1.5, legpos = (0.0,0.5), polarax=ax1,
                         label='Volume scattering phase function', legend=True)
    
    fig.tight_layout()

in the example: https://github.com/TUW-GEO/rt1/blob/master/doc/examples/example_lin_comb.ipynb.
The error information is:

Traceback (most recent call last):

  File "/Users/xushan/opt/anaconda3/envs/py310/lib/python3.10/site-packages/spyder_kernels/py3compat.py", line 356, in compat_exec
    exec(code, globals, locals)

  File "/Users/xushan/research/TUD/vodca/demo_rt1.py", line 120, in <module>
    plot1 = SRF.polarplot(inc = list(np.linspace(0,85,5)), multip = 1.5, legpos = (0.,0.5), polarax=ax1,

  File "/Users/xushan/opt/anaconda3/envs/py310/lib/python3.10/site-packages/rt1/rtplots.py", line 263, in polarplot
    return fig

UnboundLocalError: local variable 'fig' referenced before assignment

It seems that the fig is not explicitly assigned in the function rtplots.py if polarax is not None.