Nix rule breaks plugin

[ymarkus]

When I add this rule:

call lexima#add_rule({'char': "''", 'input_after': "''", 'filetype': 'nix'})

the plugin does this:
https://user-images.githubusercontent.com/62380378/141512055-74fcf878-c96b-4d6d-a55f-ae1381e0ee4b.mp4

This is the exact text it inserts:

pumvisible() ? "\{" : lexima#expand('
      ', 'i')

[cohama]

I can't repro. Please report minimal vimrc.