The default context for FhirPath evaluation is leaving out %resource

[ewoutkramer]

Is your feature request related to a problem? Please describe.
When you execute one of the extension methods for FhirPath on POCO or ITypedElement - and you don't supply the optional parameter for the context, a default, empty context is provided. This means that %resource and %rootResource will return null. Although these environment variables are not used often, they are not expected to be null. In fact, the constructor for FhirEvaluationContext that takes a ScopedNode as a parameter, will try to locate the nearest resource in the input data and then set the %resource accordingly. It makes total sense that this is the default. In fact, when we ourselves invoke the FP engine in the validator, we are always supplying the correct parameters.

Describe the solution you'd like
Pick a sensible default, instead of null. Preferably the same approach as the constructor taking ScopedNode.

[ewoutkramer]

Note that finding defaults is only possible if the caller supplies input data that is itself a resource, or a node within a ScopedNode - otherwise we won't be able to find a sensible default "resource" node within the parents of the data passed in.

[mmsmits]

See also:
#327