NoMethodError: undefined method `permit' for #<String:0x00007f887e7e4ce0>

https://sentry.gitlab.net/gitlab/devgitlaborg/issues/596103/

NoMethodError: undefined method `permit' for #<String:0x00007f887e7e4ce0>
  projects/merge_requests/application_controller.rb:17:in `merge_request_params'
    params.require(:merge_request).permit(merge_request_params_attributes)
  projects/merge_requests/creations_controller.rb:92:in `build_merge_request'
    @merge_request = ::MergeRequests::BuildService.new(project, current_user, merge_request_params.merge(diff_options: diff_options)).execute
  active_support/callbacks.rb:382:in `block in make_lambda'
    lambda { |target, _, &blk| target.send filter, &blk }
  active_support/callbacks.rb:150:in `block (2 levels) in halting_and_conditional'
    result_lambda = -> { user_callback.call target, value }
  abstract_controller/callbacks.rb:12:in `block (2 levels) in <module:Callbacks>'
    terminator: ->(controller, result_lambda) { result_lambda.call if result_lambda.is_a?(Proc); controller.performed? },
...
(131 additional frame(s) were not displayed)

NoMethodError: undefined method `permit' for #<String:0x00007f887e7e4ce0>