code: @Override
      public JavaType getInputType(TypeFactory typeFactory) {
          return typeFactory.constructMapType(HashMap.class, String.class, Headend.class);
      }
docs: Method that can be used to find out actual input (source) type; this
  usually can be determined from type parameters, but may need
  to be implemented differently from programmatically defined
  converters (which can not change static type parameter bindings).
  
  @param typeFactory
  @since 2.2