The “not equal to” operator <> returns TRUE when the two arguments do not have the same value.
A comparison between BLANK and 0 or between BLANK and an empty string returns FALSE.
Use the == operator to treat BLANK and 0 or empty string as different values.
This operator does not perform any implicit conversion between strings, numbers, and Boolean values.
The following are valid expressions using the “not equal to” operator.

Product[Color] <> "Red"
Sales[Quantity] <> 0
Customer[LargeFamily] <> TRUE

See Handling BLANK in DAX for more details about BLANK comparisons.