Leetcode上的运行时错误java.lang.ArrayIndexOutOfBoundsException

当我将代码提交给Leetcode时，它报告运行时错误为：

Runtime Error Message: Line 8: java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1 

I tested that case in my local, it works fine. I thought it maybe causeed by the platform and compiler are different. I then tried to test it on Leetcode Playground. It also worked very well. The Leetcode problem is:https://leetcode.com/problems/string-to-integer-atoi/ I would be very appreciated if anyone could let me know what's wrong with my code.

class Solution{
public int myAtoi(String str) {
        if (str == null || str.length() == 0) return 0;
        char chs[] = str.toCharArray();
        long base = 0;
        int i = 0, sign = 1;

        while (chs[i] == ' '){
                i++;
        }
        if(i == str.length()){
            return 0;
        }
        if (chs[i] == '-') {        
            i++;
            sign = -1; 
        } else if (chs[i] == '+') { 
            i++;
        }
        while (i < str.length() && (chs[i] >= '0' && chs[i] <= '9')) {
            base = base * 10 + (chs[i] - '0');
            if (sign * base > Integer.MAX_VALUE) return Integer.MAX_VALUE;
            if (sign * base < Integer.MIN_VALUE) return Integer.MIN_VALUE;
            i++;
        }
        return (int)(sign * base);
    }
}