mongodb version used : 3.4.10

instance type : t2.medium (2 cpu,4 gb ram)

present parameter settings :
"ShardingTaskExecutorPoolHostTimeoutMS" : 300000.0,
"ShardingTaskExecutorPoolMaxConnecting" : -1.0,
"ShardingTaskExecutorPoolMaxSize" : -1.0,
"ShardingTaskExecutorPoolMinSize" : 1.0,
"ShardingTaskExecutorPoolRefreshRequirementMS" : 60000.0,
"ShardingTaskExecutorPoolRefreshTimeoutMS" : 20000.0,
"connPoolMaxConnsPerHost" : 200.0,
"connPoolMaxShardedConnsPerHost" : 200.0,
"cursorTimeoutMillis" : NumberLong(600000),
"taskExecutorPoolSize" : 0.0,

I think the issue is related to ticket(https://jira.mongodb.org/browse/SERVER-25027)  but as per the documentation for version 3.4 the parameter taskExecutorPoolSize should have values from 4-64 ,I am confused as we have this parameter set to 0 

what does value 0 for  taskExecutorPoolSize parameter mean in version 3.4