UnboundLocalError: local variable 'interval' referenced before assignment

I was able to install rbp-maps using Docker using the command docker pull brianyee/rbp-maps:a5c9bd9 (but not docker pull brianyee/rbp-maps). However, I was not able to successfully run plot_map using either --ipbam for plotting density or --peak for plotting peaks.

For HPC, I need to use singularity, and this was one of my calls:
singularity run rbpmaps.sif plot_map --peak <path_to_bigbed> --annotations <path_to_SE.MATS.JC.nonoverlap.txt> <path_to_HepG2_native_cassette_exons_all> --annotation_type rmats rmats --output <path_to_png> --event se --normalization_level 0 --testnums 0 --bgnum 1 --sigtest fisher

I received the following message:
Traceback (most recent call last):
File "/opt/conda/bin/plot_map", line 11, in
load_entry_point('rbp-maps==0.1.4', 'console_scripts', 'plot_map')()
File "/opt/conda/lib/python2.7/site-packages/rbp_maps-0.1.4-py2.7.egg/maps/plot_map.py", line 548, in main
File "/opt/conda/lib/python2.7/site-packages/rbp_maps-0.1.4-py2.7.egg/maps/plot_map.py", line 104, in run_make_peak
File "/opt/conda/lib/python2.7/site-packages/rbp_maps-0.1.4-py2.7.egg/density/Map.py", line 701, in create_matrices
File "/opt/conda/lib/python2.7/site-packages/rbp_maps-0.1.4-py2.7.egg/density/matrix.py", line 562, in skipped_exon
UnboundLocalError: local variable 'interval' referenced before assignment

Start with density/matrix.py at skipped_exon, identified in the traceback, and reproduce the failure using the supplied plot_map --peak command. Check the related plot_map.py entry points for the --peak and --ipbam paths. Done means both plotting modes complete without the UnboundLocalError.