code: public Long getAsNullableLong(String key) {
  		Object value = getAsObject(key);
  		return LongConverter.toNullableLong(value);
  	}
docs: Converts map element into a long or returns null if conversion is not
  possible.
  
  @param key a key of element to get.
  @return long value of the element or null if conversion is not supported.
  
  @see LongConverter#toNullableLong(Object)