Nested FEEL path expressions resolving as `null` with `Null` type

[barinali]

Describe the Bug

As the main issue describes, the FEEL path expressions that cannot be resolved in the diagram are resolved as null with Null type which is misleading as they're not explicitly null.

Cf. #98 (comment)

Actual Behavior

• Nested FEEL path expressions resolve as null with Null type due to absence of intermediate variables/properties like =agent.foo.bar resolving as null when agent={ bar: {} }.

Expected Behavior

• Nested FEEL path expressions that cannot be explicitly resolved to a certain value should be resolved as its FEEL expression with Any type.

Additional context

I understand that it's not always the case that =agent.foo.bar should be resolved as =agent.foo.bar with Any type as it may be just misused or there's no element (a job worker or any other elements that overwrites the variable) populating the "absent" variables/properties. In those cases, we may want to actually resolve to null with Null type. However, this may be more relevant as of camunda/camunda-modeler#5697.