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String[] keys = new String[payGroupMap.size()];
Set set = payGroupMap.keySet();
Iterator iterator = set.iterator();
int i=0;
while(iterator.hasNext()){
keys[i] = iterator.next().toString();
i++;
}
Exception in thread "main" java.lang.NullPointerException
Map payGroupMap = new HashMap();
payGroupMap.put(null, "");
String[] keys = new String[payGroupMap.size()];
Set set = payGroupMap.keySet();
Iterator iterator = set.iterator();
int i=0;
while(iterator.hasNext()){
keys[i] = iterator.next().toString();
i++;
}