I'm sharing one of my most used function. It's just Wil Shipley's IsEmpty() renamed.

static inline BOOL moIsEmpty(id thing) {
    return thing == nil ||
        thing == [NSNull null] ||
        ([thing respondsToSelector:@selector(length)] && [(NSData*)thing length] == 0) ||
        ([thing respondsToSelector:@selector(count)]  && [(NSArray*)thing count] == 0);
}

Just put this into a header file and anytime you want to check if a container/string is empty — nil, [NSNull null], empty string, a container with no elements — you use moIsEmpty().

Also a convenience function wrapping it:

static inline BOOL moNotEmpty(id thing) {
    return !moIsEmpty(thing);
}

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