mutableArrayValueForKey + weak is not really weak...

mutableArrayValueForKey-weak.m

- (void)testExample {
    
    MyObject* obj = [[MyObject alloc] init];
    obj.array = @[];
    
    NSMutableArray* array = [obj mutableArrayValueForKey:@"array"];
    // NSMutableArray* array = @[].mutableCopy;    // using this will pass test
    
    __weak NSMutableArray* weakArray = array;
    
    [array addObject:@1];
    
    XCTAssertTrue([array isEqualToArray:@[@1]]);
    XCTAssertTrue([weakArray isEqualToArray:@[@1]]);
    
    array = nil;
    
    XCTAssertNil(array);
    XCTAssertNil(weakArray);    // fail: weakArray is not nil...
    
}