code: public String getFirst(String key)
      {
          if(key == null)
              throw new IllegalArgumentException("Null keys not allowed.");
  
          List<String> vals = map.get(key);
          if(vals == null || vals.size() == 0)
              return null;
  
          return vals.get(0);
      }
docs: Return the first value stored for the supplied key
  @param key The key
  @return the first value stored for the key, null if there are no values stored