Comparing different types should return null

[saig0]

Describe the bug
If I compare two values of a different type, the engine returns a failure. But it should be more friendly and return null instead.

This applies to expressions with the following operators: =, !=, <, >, etc.
And, this applies to unary-test expressions if the input value has a different type as the other value.

To Reproduce
Steps to reproduce the behavior:

1. Evaluate the following expression

"foo" = 100

2. Verify that the engine returns a failure:

failed to evaluate expression '"foo" = 100': expected String but found 'ValNumber(100)'

Expected behavior
According to the DMN spec, the comparison of different types should return null.

(DMN 1.5, chapter 10.3.2.2, page 105)

• Related TCK test case: 0068-feel-equality

Environment

• FEEL engine version: 1.16
• Affects:
  • Camunda Automation Platform 7: [7.x]
  • Zeebe broker: [0.x]