code: public static void unregisterTypeConversion(Conversion<?> conversion) {
  		if (conversion!=null) {
  			Object[] keys=conversion.getTypeKeys();
  			synchronized (typeConversions) {
  				if (keys==null) {
  					for (int i=0; i<keys.length; i++) {
  						unregisterTypeConversion(keys[i]);
  					}
  				}
  
  				for (Object key: getTypeKeys(conversion)) {
  					typeConversions.remove(key);
  				}
  			}
  		}
  	}
docs: Unregister a type conversion object under all keys it specifies via
  the {@link TypeConversion#getTypeKeys} method. Note, if this conversion
  is registered under other type keys, it will NOT be removed from those.