public StringExpression stringValue() {
        if (stringCast == null) {
            stringCast = Expressions.stringOperation(Ops.STRING_CAST, mixin);
        }
        return stringCast;
    }
Create a cast to String expression

@see java.lang.Object#toString()
@return cast expression
querydsl-core/src/main/java/com/querydsl/core/types/dsl/LiteralExpression.java