When I try to do a Min on a date field I have an error.

the code

require 'rubygems'
require 'cascading'
require 'cascading-ext/jdbc'
require 'utils'
require 'common'
require 'date'

playersource = "/home/brm/brm-current/meo_playerProfile_small.csv"
# playersource = "/home/brm/brm-current/meo_playerProfile_20090323_OVH.csv"
horsesource = "/home/brm/brm-current/meo_horse_20090323_OVH.csv" 
#cardsource = "/home/brm/brm-current/meo_card_20090323_OVH.csv" 
cardsource = "/home/brm/brm-current/meo_card_small.csv" 

output = "/home/brm/brm-current/brm-app-meo/player.dim"


flow = Cascading::Flow.new "olap" do

  source tap(cardsource)
  sink tap(output , :replace => true)
  
	assembly "main" do
		split "line", 
			:into => ["code","transactionId","playerProfile_id","valid","country","lot","subType","premium","creationTime","registrationTime","useTime","sourceCode","multiple","original_server"], 
			:pattern=>/\t/, 
			:output=> ["playerProfile_id","useTime"]
	
		filter "playerProfile_id.equals(\"NULL\")"
		group_by "playerProfile_id"
		
		# Min on Date
		every "useTime", :aggregator => Java::CascadingOperationAggregator::Min.new(Cascading.fields("first_transaction_date"))


	end		

end

the stack

brm@wormee1:~/brm-current/brm-app-meo$ ./bin/run_jobs 05-test
09/03/27 11:05:17 INFO flow.MultiMapReducePlanner: using application jar: /usr/local/share/cascading/cascading-1.0.3.jar
09/03/27 11:05:17 INFO flow.Flow: [main] starting
09/03/27 11:05:17 INFO flow.Flow: [main]  source: Hfs["TextLine[['line']->[ALL]]"]["/home/brm/brm-current/meo_card_small.csv"]"]
09/03/27 11:05:17 INFO flow.Flow: [main]  sink: Hfs["TextLine[['line']->[ALL]]"]["/home/brm/brm-current/brm-app-meo/player.dim"]"]
09/03/27 11:05:18 INFO flow.Flow: [main]  parallel execution is enabled: false
09/03/27 11:05:18 INFO flow.Flow: [main]  starting jobs: 1
09/03/27 11:05:18 INFO flow.Flow: [main]  allocating threads: 1
09/03/27 11:05:18 INFO flow.FlowStep: [main] starting step: (1/1) Hfs["TextLine[['line']->[ALL]]"]["/home/brm/brm-current/brm-app-meo/player.dim"]"]
09/03/27 11:05:18 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
09/03/27 11:05:18 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
09/03/27 11:05:18 INFO mapred.FileInputFormat: Total input paths to process : 1
09/03/27 11:05:18 INFO mapred.FileInputFormat: Total input paths to process : 1
09/03/27 11:05:18 INFO mapred.MapTask: numReduceTasks: 1
09/03/27 11:05:18 INFO mapred.MapTask: io.sort.mb = 100
09/03/27 11:05:18 INFO mapred.MapTask: data buffer = 79691776/99614720
09/03/27 11:05:18 INFO mapred.MapTask: record buffer = 262144/327680
09/03/27 11:05:18 INFO mapred.MapTask: Starting flush of map output
09/03/27 11:05:18 INFO mapred.MapTask: Finished spill 0
09/03/27 11:05:18 INFO mapred.TaskRunner: Task:attempt_local_0001_m_000000_0 is done. And is in the process of commiting
09/03/27 11:05:18 INFO mapred.LocalJobRunner: file:/home/brm/brm-current/meo_card_small.csv:0+64805
09/03/27 11:05:18 INFO mapred.TaskRunner: Task 'attempt_local_0001_m_000000_0' done.
09/03/27 11:05:18 INFO mapred.LocalJobRunner:
09/03/27 11:05:18 INFO mapred.Merger: Merging 1 sorted segments
09/03/27 11:05:18 INFO mapred.Merger: Down to the last merge-pass, with 1 segments left of total size: 1094 bytes
09/03/27 11:05:18 INFO mapred.LocalJobRunner:
09/03/27 11:05:18 WARN mapred.LocalJobRunner: job_local_0001
cascading.pipe.OperatorException: [main][sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)] operator Every failed executing aggregator: Min[decl:'first_transaction_date'][args:1]
        at cascading.pipe.Every$EveryAggregatorHandler.operate(Every.java:403)
        at cascading.flow.stack.EveryAllAggregatorReducerStackElement.operateEveryHandlers(EveryAllAggregatorReducerStackElement.java:89)
        at cascading.flow.stack.EveryAllAggregatorReducerStackElement.collect(EveryAllAggregatorReducerStackElement.java:64)
        at cascading.flow.stack.GroupReducerStackElement.operateGroup(GroupReducerStackElement.java:76)
        at cascading.flow.stack.GroupReducerStackElement.collect(GroupReducerStackElement.java:60)
        at cascading.flow.stack.FlowReducerStack.reduce(FlowReducerStack.java:152)
        at cascading.flow.FlowReducer.reduce(FlowReducer.java:77)
        at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:436)
        at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:170)
Caused by: java.lang.NumberFormatException: For input string: "2008-10-31 18:44:34"
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1224)
        at java.lang.Double.parseDouble(Double.java:510)
        at cascading.tuple.Tuple.getDouble(Tuple.java:262)
        at cascading.tuple.TupleEntry.getDouble(TupleEntry.java:286)
        at cascading.operation.aggregator.ExtremaBase.aggregate(ExtremaBase.java:111)
        at cascading.pipe.Every$EveryAggregatorHandler.operate(Every.java:399)
        ... 8 more
09/03/27 11:05:23 WARN flow.FlowStep: [main] completion events count: 0
09/03/27 11:05:23 WARN flow.Flow: stopping jobs
09/03/27 11:05:23 INFO flow.FlowStep: [main] stopping: (1/1) Hfs["TextLine[['line']->[ALL]]"]["/home/brm/brm-current/brm-app-meo/player.dim"]"]
09/03/27 11:05:23 WARN flow.Flow: stopped jobs
09/03/27 11:05:23 WARN flow.Flow: shutting down job executor
09/03/27 11:05:23 WARN flow.Flow: shutdown complete
cascading/flow/FlowStep.java:458:in `call': cascading.flow.FlowException: step failed: (1/1) Hfs["TextLine[['line']->[ALL]]"]["/home/brm/brm-current/brm-app-meo/player.dim"]"] (NativeException)
        from cascading/flow/FlowStep.java:389:in `call'
        from java/util/concurrent/FutureTask.java:303:in `innerRun'
        from java/util/concurrent/FutureTask.java:138:in `run'
        from java/util/concurrent/ThreadPoolExecutor.java:885:in `runTask'
        from java/util/concurrent/ThreadPoolExecutor.java:907:in `run'
        from java/lang/Thread.java:619:in `run'
        from ./bin/run_jobs:21
        from ./bin/run_jobs:20:in `each'
        from ./bin/run_jobs:20
Complete Java stackTrace
cascading.flow.FlowException: step failed: (1/1) Hfs["TextLine[['line']->[ALL]]"]["/home/brm/brm-current/brm-app-meo/player.dim"]"]
        at cascading.flow.FlowStep$FlowStepJob.call(FlowStep.java:458)
        at cascading.flow.FlowStep$FlowStepJob.call(FlowStep.java:389)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
        at java.lang.Thread.run(Thread.java:619)