How to ignore null data using parallel categories?

I’m attempting to utilize parallel categories but my data contains null values among some levels. In other words, not all records make it to the last level. The null values are creating separate segments at each level and the plot is misleading.

I’ve tried replacing the nulls as np.nan and None but the plot still aggregated the nulls into their own segments.

If I cannot force the plot to ignore the nulls is there a way to “hide” the null segments and adjacent links using a transparent color?