code: @Override
      public void validate() throws Exception {
          super.validate();
          this.parse();
          Assert.assertTrue(
                  String.format(
                          "Lower bound %d should be less than upper bound %d",
                          lower,
                          upper),
                  lower <= upper);
          Assert.assertFalse(
                  "The range is empty",
                  !this.includeLower
                      && !this.includeUpper
                      && (this.upper - this.lower) <= 1);
          Assert.assertFalse(
                  "The range is empty",
                  !(this.includeLower && this.includeUpper)
                      && (this.upper - this.lower) < 1);
      }
docs: /* (non-Javadoc)
  @see com.github.mkolisnyk.aerial.expressions.ValueExpression#validate()