factory error in raills

An error occurred in a before(:suite) hook. Failure/Error: FactoryGirl.lint

FactoryGirl::InvalidFactoryError: The following factories are invalid:

• invoice - nil can't be coerced into Fixnum (TypeError)
• paid_invoice - nil can't be coerced into Fixnum (TypeError)
• receipt - nil can't be coerced into Fixnum (TypeError)
• refund_receipt - nil can't be coerced into Fixnum (TypeError)

  /usr/local/rvm/gems/ruby-2.3.0@carve/gems/factory_girl-4.8.0/lib/factory_girl/linter.rb:12:in `lint!'

/usr/local/rvm/gems/ruby-2.3.0@carve/gems/factory_girl-4.8.0/lib/factory_girl.rb:67:in `lint'

./spec/support/factory_girl.rb:13:in `block (2 levels) in '

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