docs: <T> Collection<Method> getPrimaryKeyGetters(Class<T> clazz) {
          synchronized (primaryKeyGettersCache) {
              if ( !primaryKeyGettersCache.containsKey(clazz) ) {
                  List<Method> keyGetters = new LinkedList<Method>();
                  for (Method getter : getRelevantGetters(clazz)) {
                      if (ReflectionUtils.getterOrFieldHasAnnotation(getter, DynamoDBHashKey.class)
                          || ReflectionUtils.getterOrFieldHasAnnotation(getter, DynamoDBRangeKey.class)) {
                          keyGetters.add(getter);
                      }
                  }
                  primaryKeyGettersCache.put(clazz, keyGetters);
              }
              return primaryKeyGettersCache.get(clazz);
          }
      }