For API#initialize, set context to link header only if the document doesn't define a context, and one is not passed.
For API#initialize, set context to link header only if the document doesn't define a context, and one is not passed.

ruby-rdf/json-ld,gkellogg/json-ld,ruby-rdf/json-ld,PerfectMemory/json-ld,PerfectMemory/json-ld