Splits a given string into an array of substrings based on newline characters.
If the input is undefined, the function returns undefined.
The string to be split by newline characters. Can be undefined.
An array of substrings if the input is a string, or undefined if the input is undefined.
Splits a given string into an array of substrings based on newline characters. If the input is
undefined, the function returnsundefined.