mapAB4 edge cases

while trying below challenge
http://codingbat.com/prob/p136950

i wrote my code as below

public Map<String, String> mapAB4(Map<String, String> map) {
   if( map.get("a")!=null && map.get("b")!=null && map.get("a").length()> map.get("b").length() ){
    map.put("c",map.get("a"));
    
  }
    if( map.get("a")!=null && map.get("b")!=null && map.get("b").length()> map.get("a").length() ){
    map.put("c",map.get("b"));
    
  }
   if( map.get("a")!=null && map.get("b")!=null && map.get("a").equals(map.get("b")) ){
    map.put("a","");
    map.put("b","");
  }
  
  if( map.get("a")!=null && map.get("b")!=null && map.get("a").equals(map.get("b")) ){
    map.put("a","");
    map.put("b","");
  }
  return map;
}

Select allOpen in new window

i am failing below tests

Expected      Run            
mapAB4({"a": "aaa", "b": "bb", "c": "cake"}) → {"a": "aaa", "b": "bb", "c": "aaa"}      {"a": "aaa", "b": "bb", "c": "aaa"}      OK      
mapAB4({"a": "aa", "b": "bbb", "c": "cake"}) → {"a": "aa", "b": "bbb", "c": "bbb"}      {"a": "aa", "b": "bbb", "c": "bbb"}      OK      
mapAB4({"a": "aa", "b": "bbb"}) → {"a": "aa", "b": "bbb", "c": "bbb"}      {"a": "aa", "b": "bbb", "c": "bbb"}      OK      
mapAB4({"a": "aaa"}) → {"a": "aaa"}      {"a": "aaa"}      OK      
mapAB4({"b": "bbb"}) → {"b": "bbb"}      {"b": "bbb"}      OK      
mapAB4({"a": "aaa", "b": "bbb", "c": "cake"}) → {"a": "", "b": "", "c": "cake"}      {"a": "aaa", "b": "bbb", "c": "cake"}      X      
mapAB4({"a": "a", "b": "b", "c": "cake"}) → {"a": "", "b": "", "c": "cake"}      {"a": "a", "b": "b", "c": "cake"}      X      
mapAB4({"a": "", "b": "b", "c": "cake"}) → {"a": "", "b": "b", "c": "b"}      {"a": "", "b": "b", "c": "b"}      OK      
mapAB4({"a": "a", "b": "", "c": "cake"}) → {"a": "a", "b": "", "c": "a"}      {"a": "a", "b": "", "c": "a"}      OK      
mapAB4({"c": "cat", "d": "dog"}) → {"c": "cat", "d": "dog"}      {"c": "cat", "d": "dog"}      OK      
mapAB4({"ccc": "ccc"}) → {"ccc": "ccc"}      {"ccc": "ccc"}      OK      
mapAB4({"c": "a", "d": "b"}) → {"c": "a", "d": "b"}      {"c": "a", "d": "b"}      OK      
mapAB4({}) → {}      {}      OK      
mapAB4({"a": "", "z": "z"}) → {"a": "", "z": "z"}      {"a": "", "z": "z"}      OK      
mapAB4({"b": "", "z": "z"}) → {"b": "", "z": "z"}      {"b": "", "z": "z"}      OK      
other tests
OK      
Correct for more than half the tests

Your progress graph for this problem

how to improve my code and fix the tests.

please advise