Includes returns false instead of null if either operand is null

[bryantaustin13]

To dupe:

<?xml version="1.0" encoding="utf-8"?>
<tests xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://hl7.org/fhirpath/tests" xsi:schemaLocation="http://hl7.org/fhirpath/tests ../../testSchema/testSchema.xsd"
	   name="CqlListOperatorsTest">
	<group name="SingleTest" version="1.0">
		<test name="IncludesNullLeft" version="1.0">
			<capability code="list-operators" />
			<expression>null includes {2}</expression>
			<output>null</output>
		</test>
	</group>
</tests>

actual: false

According to https://cql.hl7.org/09-b-cqlreference.html#includes "For the interval-interval overload, if either argument is null, the result is null."
This actually is slightly ambiguous because it only specifically states interval-interval, but one could infer that it applies to all.

[bryantaustin13]

Moved to clinical_quality_language #1718