code: public static Expression<String> toLower(Expression<String> stringExpression) {
          if (stringExpression instanceof Constant) {
              Constant<String> constantExpression = (Constant<String>) stringExpression;
              return ConstantImpl.create(constantExpression.getConstant().toLowerCase());
          } else {
              return operation(String.class, Ops.LOWER, stringExpression);
          }
      }
docs: Converts the given expression to lower(expression)
  
  <p>Constants are lower()ed at creation time</p>
  
  @param stringExpression the string to lower()
  @return lower(stringExpression)