hashmap - Java multikeymap put-method -

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I put in Java for a multimimate and applied methods with two keys pointing to a value Want to do I have written this way: 

  public value type type (keypie key 1, keytype key key 2, value type value) {Hashmap < Ketip B, Value Type & gt; Mappi = outerMap.get (key1); ValueType Old Price; If (mappi.containsKey (key2)) {oldvalue = mappi.get (key2); } Else {oldvalue = null; }

However, when I test this method (I have started the map properly as my own multi-type type) 

  mappi.put "xxxxx", 13, "xxxxx"); I get a NullPointerException at

me 

  (if mappi.containsKey (key2)) {  
 what is the reason Exceptions? In my class multicomap I initialize the multimimize object into the constructor, so it should be fine.   
 
 
 If this is not a homework, you can use it, instead of resuming it from scratch .  
 To answer your question, I suspect that in error  hashmap and lieutenant; Ketip B, Value Type & gt; Mappi = outerMap.get (key1); . If there is no value in key 1 in  external mark , then  mappi  will be zero, from which  NullPointerException

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