When i am trying to fetch information about OutOfOfficeMessage field from user by using query i didnt get any result..how should i get the results

IF i try this query i get expected result [ SELECT Id, OutOfOfficeMessage,Alias FROM User ]

but i need result with this query and it doesn't give results , but it has to be show results

[ SELECT Id, OutOfOfficeMessage,Alias FROM User WHERE OutOfOfficeMessage != null ]

Note : OutOfOfficeMessage  is text field in User Object

#Data Management