Given a singular English noun in lowercase, return its plural form by applying these rules in order:
- If the noun ends with ch or sh, add es (church becomes churches, dish becomes dishes)
- If the noun ends with s, x, or z, add es (bus becomes buses, box becomes boxes)
- If the noun ends with a consonant followed by y, replace the y with ies (city becomes cities, baby becomes babies)
- If the noun ends with a vowel followed by y, add s (day becomes days, boy becomes boys)
- Otherwise, add s (cat becomes cats)
Return null for null input and an empty string for empty input.
Examples:
Input: noun = 'cat'
Output: 'cats'
Explanation: Regular noun, add s
Input: noun = 'bus'
Output: 'buses'
Explanation: Ends in s, add es
Input: noun = 'city'
Output: 'cities'
Explanation: Consonant before y, replace y with ies
Input: noun = 'day'
Output: 'days'
Explanation: Vowel before y, add s
Input: noun = 'church'
Output: 'churches'
Explanation: Ends in ch, add es
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