public void expectSpecific() {
      if (this == ALL_CATEGORIES) {
        throw new IllegalArgumentException(
          "Expected a specific block " + "category but got " + this);
      }
    }
Throws an exception if the block category passed is the special category meaning "all
categories".
hbase-common/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockType.java