code: public static <A, B> Map<A, B> removeNullEntries(Map<A, B> map) {
  
          HashMap<A, B> result = new HashMap<A, B>();
  
          for (Map.Entry<A, B> entry : map.entrySet()) {
              if (entry.getValue() != null) {
                  result.put(entry.getKey(), entry.getValue());
              }
          }
          return result;
      }
docs: Returns a new map with all entries of the input map except those which have a value of null.<p>
  
  @param <A> the key type of the map
  @param <B> the value type of the map
  @param map the input map
  
  @return a map with all null entries removed