Method invocation may produce 'NoMethodError'

[tit]

I use RubyMine IDE and gem HTTPClient.

# frozen_string_literal: true

require 'httpclient'

client = HTTPClient.new
response = client.get 'https://httpbin.org/get'

body = response.body # <<- SEE HERE

puts body

Why RubyMine have warning about Method invocation may produce 'NoMethodError'?