我对Cassandra的世界还很陌生。我使用cqlsh创建了一个cassandra表，如下所示：

CREATE TABLE "userRecommendations" (uid text PRIMARY KEY, app set<text>);

现在，当我使用cassandra cli describe keySpace; ，我明白了

[default@keySpace] describe userRecommendations;
ColumnFamily: userRecommendations
  Key Validation Class: org.apache.cassandra.db.marshal.UTF8Type
  Default column value validator: org.apache.cassandra.db.marshal.BytesType
  Columns sorted by: org.apache.cassandra.db.marshal.CompositeType(org.apache.cassandra.db.marshal.UTF8Type,org.apache.cassandra.db.marshal.ColumnToCollectionType(617070:org.apache.cassandra.db.marshal.SetType(org.apache.cassandra.db.marshal.UTF8Type)))
  GC grace seconds: 0
  Compaction min/max thresholds: 0/0
  Read repair chance: 0.0
  DC Local Read repair chance: 0.0
  Populate IO Cache on flush: false
  Replicate on write: false
  Caching: keys_only
  Bloom Filter FP chance: default
  Built indexes: []
  Compaction Strategy: null
null

然后，如果我在列族上做了一个操作，我会得到一个例外。

[default@UserInfo] get userRecommendations[utf8('aparna')][utf8('app')];
Not enough bytes to read value of component 0
InvalidRequestException(why:Not enough bytes to read value of component 0)
    at org.apache.cassandra.thrift.Cassandra$get_result.read(Cassandra.java:6592)
    at org.apache.thrift.TServiceClient.receiveBase(TServiceClient.java:78)
    at org.apache.cassandra.thrift.Cassandra$Client.recv_get(Cassandra.java:556)
    at org.apache.cassandra.thrift.Cassandra$Client.get(Cassandra.java:541)
    at org.apache.cassandra.cli.CliClient.executeGet(CliClient.java:723)
    at org.apache.cassandra.cli.CliClient.executeCLIStatement(CliClient.java:210)
    at org.apache.cassandra.cli.CliMain.processStatementInteractive(CliMain.java:210)
    at org.apache.cassandra.cli.CliMain.main(CliMain.java:337)

我做错了什么？
提前多谢！