String Window, what am i getting this run-error?

#1

Output :

TESTCASE # 1 : run-error (Time: 0.06 s)
TESTCASE # 2 : run-error (Time: 0.06 s)
TESTCASE # 3 : run-error (Time: 0.06 s)
TESTCASE # 4 : correct (Time: 0.05 s)
TESTCASE # 5 : run-error (Time: 0.06 s)
TESTCASE # 6 : correct (Time: 0.06 s)
TESTCASE # 7 : correct (Time: 0.07 s)
TESTCASE # 8 : correct (Time: 0.06 s)
TESTCASE # 9 : run-error (Time: 0.06 s)
TESTCASE # 10 : correct (Time: 0.06 s)

I submitted same solution on leetcode and it got accepted;