code: public static <T> DataKey<T> create(String name, GenericType<T> genType, boolean allowNull) {
          return create(name, genType.getRawType(), allowNull, null);
      }
docs: creates a data key with the given name, data type and the given permission
  to allow null values. No default value will be specified.
  
  @param <T> the type
  @param name the name of the key that is stored in the xdata file
  @param genType the type's class' generic type
  @param allowNull allow null values?
  @return