### 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.value(),
                                            range.lower(),
                                            range.includeLower(),
                                            range.upper(),
                                            false,
                                            range.zoneId()
                                        )
                                    );
                                }
                                
                                
                                return true;
                            }
                            
                            
                        }
                    } 
                    comp = range.upper().foldable() ? BinaryComparison.compare(neqVal, range.upper().fold()) : null;
                    if (comp != null && comp >= 0) {
                        if (comp == 0 && range.includeUpper()) { 
                            ranges.set(
                                i,
                                new Range(
                                    range.source(),
                                    range.value(),
                                    range.lower(),
                                    range.includeLower(),
                                    range.upper(),
                                    false,
                                    range.zoneId()