### Description

The IS NULL/IS NOT NULL only care about the nullability not the value of an expression.
Given the expression x + 1 / 2, the actual result does not matter only if it's null or not - that is, it only matters if x is null or not.
So x + 1 / 2 IS NULL becomes x IS NULL - which can be opportunistically pushed down or evaluated.
x-pack/plugin/ql/src/main/java/org/elasticsearch/xpack/ql/optimizer/OptimizerRules.java
range.lower(),
                                        range.includeLower(),
                                        range.upper(),
                                        true,
                                        range.zoneId()
                                    )
                                );
                            } 
                            removeEquals = true; 
                            break;
                        } else if (lowerComp != null && upperComp != null) {
                            if (0 < lowerComp && upperComp < 0) { 
                                removeEquals = true; 
                                break;
                            }
                        }
                    }
                }
                if (removeEquals) {
                    iterEq.remove();
                    updated = true;
                    continue;
                }
                
                for (int i = 0; i < inequalities.size(); i++) {
                    BinaryComparison bc = inequalities.get(i);
                    if (eq.left().semanticEquals(bc.left())) {
                        Integer comp = BinaryComparison.compare(eqValue, bc.right().fold());
                        if (comp != null) {
                            if (bc instanceof GreaterThan || bc instanceof GreaterThanOrEqual) {