DMN DT Analysis include `null` for gaps/overlaps calculation where possible.

Implemented with considering a `null` value on a given a dimension:

• not "filling" Gaps on the other dimensions
• not causing Overlaps on the other dimensions

For example, in a table such as:

Rule2 is not overlapping with Rule1, as they don't overlap on dimension/In1 not for a range not for a singularity value.
Rule2 is not "filling" any gaps either, as for Rule2 is not spanning for dimension/In1 in the range [-Inf, 0], it cannot be a candidate to fill any gaps where in dimension/In2 >=0
Therefore the overall analysis for this table still is:

Gaps:
[ -Inf .. 0 ) ( 0 .. +Inf ]
[ 0 .. 0 ] [ 0 .. +Inf ]
( 0 .. +Inf ] [ -Inf .. 0 )