Defaulting parameters to false

I'm unclear how you are using dump = false and whether the method returns anything more than nil when params[:dump] is unassigned. If it doesn't, I would recommend the use of a guard clause:

def report
  return unless params[:dump]
  data = {}
  render :json => p(data)
end

You may use the coalesce gem as mentioned in this SO answer.

def report
    dump = params[:dump]._? false

    data = {}

    if dump != false
        return render :json => p(data)
    end
end

Though I believe it would be more idiomatic to just use the falsyness of nil like this:

def report
    dump = params[:dump]
    data = {}

    if dump
        return render :json => p(data)
    end
end

This is a common pattern in Rails, so common that there is a Ruby Objct extension for it called presence.

Returns the receiver if it's present otherwise returns nil. object.presence is equivalent to

object.present? ? object : nil

In your case, the code will be changed from

dump = params[:dump] ? params[:dump] : 'false'

to

dump = params[:dump].presence || false

It's hard to refactor the entire code, because it's not clear what should happen in case the parameter is false. I assume you may want to display an error.

If that's the case, there is also another way: use an exception, or even better, reuse require from the Rails strong parameters feature, which is based on exceptions

dump = params.require(:dump)

This line alone, will allow you to get rid of the entire body.

def report
  dump = params.require(:dump)

  data = {}
  render :json => p(data)
end

If the parameter is missing, an exception ActionController::ParameterMissing is raised. You can rescue it in the app, and show the proper message.

rescue_from ActionController::ParameterMissing, with: :handle_parameter_missing

def handle_parameter_missing(exception)
  # do what you want
end

Pure ruby is your friend here :

dump = params.fetch(:dump, false)

see the docs for more info.

note : If you get an emtpy string from your params, in this case I usually find it more relevant to change the markup to avoid the need for .presence calls. This is a matter of taste ; all things considered, in ruby any object other than nil and false is truthy, so I think it is coherent with ruby's 'spirit' to avoid passing meaningless params at all.