Find the length of the longest substring without repeating characters in a given string. Return the maximum length as an Integer. For null or empty strings, return 0.

Examples:

Input: s = 'abcabcbb' Output: 3 Explanation: The longest substring without repeating characters is 'abc', with length 3. Input: s = 'bbbbb' Output: 1 Explanation: The longest substring is 'b', with length 1. Input: s = 'pwwkew' Output: 3 Explanation: The longest substring is 'wke', with length 3. Note that 'pwke' is not valid because it is not a substring. Input: s = '' Output: 0 Explanation: Empty string has no characters. Input: s = null Output: 0 Explanation: Null string returns 0. Input: s = 'abcdef' Output: 6 Explanation: The entire string has no repeating characters.
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