Given two strings s1 and s2, return true if s2 is a rotation of s1. A rotation is formed by taking some number of characters from the beginning of a string and moving them to the end. For example, "cdeab" is a rotation of "abcde" because moving "ab" from the front to the end produces "cdeab". Return false if either input is null or if the strings have different lengths.
Examples:
Input: s1 = 'abcde', s2 = 'cdeab'
Output: true
Explanation: 'cdeab' is formed by moving 'ab' from the front of 'abcde' to the end
Input: s1 = 'abc', s2 = 'bca'
Output: true
Explanation: 'bca' is a left rotation of 'abc' by one position
Input: s1 = 'abc', s2 = 'abcd'
Output: false
Explanation: The strings have different lengths so s2 cannot be a rotation of s1
Input: s1 = null, s2 = 'abc'
Output: false
Explanation: Null input returns false
Input: s1 = 'abc', s2 = 'xyz'
Output: false
Explanation: 'xyz' is not a rotation of 'abc'
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