Swift: how to set AnyObject to nil or equivalent

I have a very generic function which needs to return AnyObject:

func backgroundFunction(dm : DataManager) -> AnyObject {
    ...
}

however there are some cases where I would like to return an empty/null value

I thought about these two values:

• nil

but it doesn't seem to be allowed: Type 'AnyObject' does not conform to protocol 'NilLiteralConvertible'

• 0

but when I test if that AnyObject value is 0 with value != 0 I get this error: Binary operator '!=' cannot be applied to operands of type 'AnyObject' and 'nil'

Is there any solution?