Given a non-negative integer, count the number of trailing zeros in its decimal representation. Trailing zeros are zeros at the end of the number before any non-zero digit. Return 0 for the integer 0 and return null for null input.
Examples:
Input: num = 1200
Output: 2
Explanation: The number ends with two zeros
Input: num = 123
Output: 0
Explanation: No zeros at the end
Input: num = 10000
Output: 4
Explanation: The number ends with four zeros
Input: num = 0
Output: 0
Explanation: Zero has no trailing zeros by definition
Input: num = null
Output: null
Explanation: Null input returns null
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