code: @NonNull
      public Expression subtract(@NonNull Expression expression) {
          if (expression == null) {
              throw new IllegalArgumentException("expression cannot be null.");
          }
          return new BinaryExpression(this, expression, BinaryExpression.OpType.Subtract);
      }
docs: Create a subtract expression to subtract the given expression from the current expression.
  
  @param expression an expression to subtract from the current expression.
  @return a substract expression.