Isogram


An Isogram is word in which no letter of the alphabet occurs more than once.
(In some cases it may mean that all letters in a word or phrase occur an equal amount of times. ) For the purpose of this puzzle..
Determine if is true there being no letter in the word or phrase occurs more than once case insensitive, by implementing the eachLetterOccursOnlyOnce() method Assume that a null or empty string is true and ignore spaces & non alphabetic characters .

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