Cannot encode fasta to BioSequences.DNAAlphabet when N present

[pdimens]

Hello, I'm trying to go through the tutorial/example in the docs and I'm using a D. melanogaster genome instead of the E. coli one (it's what I have on hand). I cannot seem to get Pseudoseq to load the fasta file into Molecules() unless I remove N characters, which in my case I replaced them with A.

The genome is a pretty normal genome and the only funky in it is 7 N nucleotides. It's pretty normal to have N's in an assembly (although I expect they are less useful in simulation context). Is the intolerance of N nucleotides specific to Pseudoseq or FASTX/BioSequences?