More detailed error message

[alexisc0le]

Is your feature request related to a problem? Please describe.
I was getting a very confusing error response that seemed unrelated to the actual issue that was occurring. When I did a Questionnaire$populate on postman, I got the following error - "HAPI-0389: Failed to call access method: java.lang.IllegalArgumentException: Url http://hl7.org/fhir/StructureDefinition/questionnaireresponse-author must have only one match". In this case the questionnaire item was referencing a CQL expression that returned a list of strings, but the questionnaire item type was expecting a string.

Describe the solution you'd like
A better error message from engine that states the CQL statement and questionnaire statement are searching for different things.

Describe alternatives you've considered
The engine creates a concatenation of strings when there are multiple in one resource