TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

[Daisy19990202]

I input a code like this:
deeparg predict --model LS --type nucl -i megahit/disUV_contigs_megahit.fa -o deeparg.out
but it turns out a TypeError:deeparg predict --model LS --type nucl -i megahit/disUV_contigs_megahit.fa -o deeparg.out
I'm confused if there is any mistakes of my code or my input file?It would be so nice of you to give me a hand.