Don't fail a range comparison in FEEL when a unary test range is used

[bncriju]

There is a DMN TCK failure, when running with Drools:

[ERROR] 0068-feel-equality-test-01.range_010 – Time elapsed: 0.016 s <<< ERROR!
java.lang.RuntimeException: ERROR: FAILURE: 'range_010' expected='false' but found='null'

The test is located here (1). Based on the error, it looks like the engine fails the evaluation on an exception somewhere. It should behave based on the definition in the test and return false.

Options how to debug:

Replicating the test case directly in Drools repository, so it gets a proper stack trace pointing to the code path being executed, to be able to see the code areas, which may need a fix. If the test case is mainly just a FEEL expression (FEEL is a language used to write expressions in DMN), the FEEL expression could be added to a test class, e.g. this one (2), so it can be run in isolation.

(1) https://github.com/dmn-tck/tck/blob/master/TestCases/compliance-level-3/0068-feel-equality/0068-feel-equality.dmn#L1311

(2) https://github.com/apache/incubator-kie-drools/blob/16897949cb6b691ec6b919cd4593288ebbd00cee/kie-dmn/kie-dmn-feel/src/test/java/org/kie/dmn/feel/runtime/FEELRangesTest.java#L36

[yesamer]

range_010
range_011
range_012

Those 3 tests are failing in 0068 suite test.