Error generating code for schema with unions

[sav007]

Tried to run generation tool against Github Schema got next message:

graphql_schema.rb:203:in `fields': undefined method `map' for nil:NilClass (NoMethodError)
Did you mean?  tap
	from .../templates/APISchema.java.erb:85:in `block in generate'
	from .../templates/APISchema.java.erb:68:in `each'
	from .../templates/APISchema.java.erb:68:in `generate'
	from /opt/rubies/2.3.3/lib/ruby/2.3.0/erb.rb:864:in `eval'
	from /opt/rubies/2.3.3/lib/ruby/2.3.0/erb.rb:864:in `result'
	from .../lib/graphql_java_gen.rb:31:in `generate'
	from.../graphql_java_gen.rb:27:in `save'

The error doesn't tell what type caused the issue.

[dylanahsmith]

Looks like it is a bug in how unions are generated. That wasn't never tested well since we haven't used unions.