Fix 'Container is falsy' bug due to Babel upgrade #1293

Job	Run time
PostGraphile v4 queries tests (exported as graphql-js) / build (12, 20.x)	16m 34s
PostGraphile polymorphic query tests / build (12, 20.x)	3m 19s
@dataplan/pg tests / build (12, 20.x)	3m 40s
PostGraphile polymorphic query tests (exported as typeDefs) / build (12, 20.x)	6m 44s
PostGraphile v4 queries tests / build (12, 20.x)	3m 54s
PostGraphile mutation tests / build (12, 20.x)	3m 39s
PostGraphile mutation tests (exported as graphql-js) / build (12, 20.x)	9m 25s
PostGraphile v4 queries tests (exported as typeDefs) / build (12, 20.x)	13m 6s
PostGraphile mutation tests (exported as typeDefs) / build (12, 20.x)	7m 54s
PostGraphile polymorphic query tests (exported as graphql-js) / build (12, 20.x)	7m 57s
PostGraphile schema tests / build (12, 20.x)	6m 28s
Small package tests / build (12, 20.x)	3m 14s
	1h 25m 54s

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