code: @NonNull
      public Expression greaterThan(@NonNull Expression expression) {
          if (expression == null) {
              throw new IllegalArgumentException("expression is null");
          }
          return new BinaryExpression(this, expression, BinaryExpression.OpType.GreaterThan);
      }
docs: Create a greater than expression that evaluates whether or not the current expression
  is greater than the given expression.
  
  @param expression the expression to compare with the current expression.
  @return a greater than expression.