private ResultList evaluateLhsSingleAndRhsList(Object lhs, AttributeNode.VariableValueList rhs) {
        return evaluateOneSideListOnly(rhs, lhs, (val) -> evaluateBool(lhs, val));
    }
Evaluates a binary comparison where one or both operands are null.
Boolean outcomes are only defined for (in)equality relations, all others
return Result.INVALID.

Precondition: lhs AND/OR rhs is null.
document/src/main/java/com/yahoo/document/select/rule/ComparisonNode.java