@Override
    public BooleanExpression not() {
        if (not == null) {
            // uses this, because it makes unwrapping easier
            not = Expressions.booleanOperation(Ops.NOT, this);
        }
        return not;
    }
Create a {@code !this} expression

<p>Returns a negation of this boolean expression</p>

@return !this
querydsl-core/src/main/java/com/querydsl/core/types/dsl/BooleanExpression.java