public StringExpression upper() {
        if (upper == null) {
            upper = Expressions.stringOperation(Ops.UPPER, mixin);
        }
        return upper;
    }
Create a {@code this.toUpperCase()} expression

<p>Get the upper case form</p>

@return this.toUpperCase()
@see java.lang.String#toUpperCase()
querydsl-core/src/main/java/com/querydsl/core/types/dsl/StringExpression.java