RSpec

Fix nullstore serializer #2124

Job	Run time
rspec (3.1, gemfiles/graphql_2_1_4.gemfile)	10s
rspec (3.1, gemfiles/graphql_2_4_8.gemfile)	14s
rspec (3.2, gemfiles/graphql_2_1_4.gemfile)	16s
rspec (3.2, gemfiles/graphql_2_3_0.gemfile)	17s
rspec (3.2, gemfiles/graphql_2_3_11.gemfile)	11s
rspec (3.2, gemfiles/graphql_2_4_8.gemfile)	16s
rspec (3.2, gemfiles/graphql_master.gemfile)	19s
rspec (3.3, gemfiles/graphql_2_1_4.gemfile)	12s
rspec (3.3, gemfiles/graphql_2_3_0.gemfile)	12s
rspec (3.3, gemfiles/graphql_2_3_11.gemfile)	11s
rspec (3.3, gemfiles/graphql_2_4_8.gemfile)	15s
rspec (3.3, gemfiles/graphql_master.gemfile)	18s
rspec (3.4, gemfiles/graphql_2_1_4.gemfile)	15s
rspec (3.4, gemfiles/graphql_2_3_0.gemfile)	13s
rspec (3.4, gemfiles/graphql_2_3_11.gemfile)	11s
rspec (3.4, gemfiles/graphql_2_4_8.gemfile)	11s
rspec (3.4, gemfiles/graphql_master.gemfile)	14s
	3m 55s

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