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