How to remove key from nsmutabledictionary When value of that key is empty or null in ios?

Question

I have created NSMutableDictionary and the values of keys are formed as nsarray. I have removed objects of keys. I have no doubt for this case. But I would like to remove key When value of that key is empty or null as following as the case.

{
    Africa =     (
        "Kenya",
        "South Africa"
    );
    America =     (
    );
    Asia =     (
        "India"
    );
}

The above dictionary has three keys and one of these keys has no objects that is America. I would like remove this key. Is it possible? Can we remove key from nsmutabledictionary?

Please help me.....

Edited: Simple mistake. I understand what i have mistaken. The key(America) has value and which is empty array that means the number of elements in array is zero.