Rails generator pluralizes spec name

[Javix]

Recently I was surprised that when running 

rais g rspec:feature customer_search

RSpec generator pluralized it as folows:

Expected string default value for '--jbuilder'; got true (boolean)

      create  spec/features/customer_searches_spec.rb

Is it normal behaviour ? Relish docs say nothing (which option available, how to skip, etc.) about it.

I used RSpec 3.5.4 version.

Thank you.