java - Treemap get throws NullPointerException -

follwing java class testentry.java

private void initializemaptest()     {         eventmap = new treemap<string,string>();          //put value eventmap          maptest = new treemap<string, string>( new comparator<string>()         {             public int compare( string key1, string key2 )             {                if( key1 == null )                 {                     if( key2 == null )                     {                         return 0;                     }                     else                     {                         return 1;                     }                 }                 else                 {                     if( key2 == null )                     {                         return -1;                     }                     else                     {                         return key1.compareto( key2 );                     }                 }             }         } );          for( string s : eventmap.keyset() )         {             maptest.put( eventmap.get( s ), s );   //error @ line         }      } 

as per knowledge eventmap doesnot allow null values, hence keyset of eventmap not have null values, if value of key in eventmap null, while try put in maptest, shoukd not throw null pointer exception, because respective comparator allows null values

but why getting exception

       java.lang.nullpointerexception         @ java.util.treemap.cmp(treemap.java:1911)         @ java.util.treemap.get(treemap.java:1835)         @ kidiho.sa.client.reports.reportentry.initializemaptest(testentry.java:22) 

it throw nullpointerexception because in treemap api get() method throwing nullpointerexception deliberately if null.

final entry<k,v> getentry(object key) {         // offload comparator-based version sake of performance         if (comparator != null)             return getentryusingcomparator(key);         if (key == null)             throw new nullpointerexception();         comparable<? super k> k = (comparable<? super k>) key;         entry<k,v> p = root;         while (p != null) {             int cmp = k.compareto(p.key);             if (cmp < 0)                 p = p.left;             else if (cmp > 0)                 p = p.right;             else                 return p;         }         return null;     }