Except Time List and Except DateTime List return single instead of a list

[bryantaustin13]

This also occurs with union ("expression": "{ null } union { null }" returns a single null )
and Coalesce ("expression": "Coalesce({'a'},null, null)")
Also in StgringOperators Split "expression": "Split('a,b', null)", and "Split('a,b', '-')"

Steps 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="ExceptDateTimeList" version="1.0">
			<capability code="list-operators" />
			<expression>{ DateTime(2012, 5, 10), DateTime(2014, 12, 10), DateTime(2010, 1, 1)} except {DateTime(2014, 12, 10), DateTime(2010, 1, 1) }</expression>
			<output>{@2012-05-10T}</output>
		</test>
	</group>
</tests>

actual: "@2012-05-10T"