code: public BooleanExpression isEmpty() {
          if (isempty == null) {
              isempty = Expressions.booleanOperation(Ops.STRING_IS_EMPTY, mixin);
          }
          return isempty;
      }
docs: Create a {@code this.isEmpty()} expression
  
  <p>Return true if this String is empty</p>
  
  @return this.isEmpty()
  @see java.lang.String#isEmpty()