Empty collection comparison

[antvaset]

In FHIRPath, {} = {} is expected to evaluate to {} (an empty collection) as per the spec and FHIRPath tests.

The existing CQL test here contradicts the FHIRPath test and should be changed to expect an empty collection. null fits here well. This is already implemented in the Java engine.

[bryantaustin13]

Close this as solved when PR #130 (comment) is merged.