def NE(x=None, y=None):
if x is None and y is None:<EOL><INDENT>return {'<STR_LIT>': []}<EOL><DEDENT>return {'<STR_LIT>': [x, y]}<EOL>
Compares two values and returns:
    true when the values are not equivalent.
    false when the values are equivalent.
See https://docs.mongodb.com/manual/reference/operator/aggregation/ne/
for more details
:param x: first value or expression
:param y: second value or expression
:return: Aggregation operator