class ThisClass
  def this_method
    @something_here = { :this => 'defined' }
  end
end

class ThatClass
  def that_method
    @something_here[:that] = 'defined'
  end
end

this = ThisClass.new
this.this_method

that = ThatClass.new
that.that_method

Line 9:in `that_method': undefined method `[]=' for nil:NilClass (NoMethodError)
	from t.rb:17