Given a list of strings, return the longest common prefix shared by all strings. If there is no common prefix, return an empty string. If the input list is null, return null. If the input list is empty, return an empty string. A list containing a single element returns that element as the prefix.
Examples:
Input: strs = ['flower', 'flow', 'flight']
Output: 'fl'
Explanation: All three strings start with fl.
Input: strs = ['dog', 'racecar', 'car']
Output: ''
Explanation: There is no shared prefix among the strings.
Input: strs = ['interspecies', 'interstellar', 'interstate']
Output: 'inters'
Explanation: The longest shared prefix is inters.
Input: strs = ['alone']
Output: 'alone'
Explanation: A single string is its own longest prefix.
Input: strs = null
Output: null
Explanation: Null input returns null.
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