Take a string and return a Map<String, Integer> where each key is a character and each value is how many times that character appears. Ignore case (treat 'A' and 'a' as the same). Return an empty map for null or empty strings.
Examples:
Input: text = "hello"
Output: {'h':1, 'e':1, 'l':2, 'o':1}
Explanation: The character 'l' appears twice, all others appear once
Input: text = "AaBb"
Output: {'a':2, 'b':2}
Explanation: Case insensitive, so 'A' and 'a' count as the same character
Input: text = "hello world"
Output: {'h':1, 'e':1, 'l':3, 'o':2, ' ':1, 'w':1, 'r':1, 'd':1}
Explanation: All characters including spaces are counted
Input: text = null
Output: {}
Explanation: Returns empty map for null input
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