Getting Error while using SinceDB in azure blob plugin.

I am using AzureBlob Plugin to pull the logs of NSG Flow Logs and Azure ActivityLogs to the same ELK instance. My Plugin Input Configuration for the following Logs are as follows.
**NSG Flow Logs:**
input {
azureblob
{
storage_account_name => "test1"
storage_access_key => "xxxxxxxxxxxxxxx"
container => "insights-logs-networksecuritygroupflowevent"
codec => "json"
type => "nsg_flow_logs"
# Refer https://docs.microsoft.com/en-us/azure/network-watcher/network-watcher-read-nsg-flow-logs
# Typical numbers could be 21/9 or 12/2 depends on the nsg log file types
file_head_bytes => 12
file_tail_bytes => 2
sincedb => "/usr/share/logstash/data/nsg_flow_logs_sincedb"
}
}

**For Azure Activity Logs:**
input {
azureblob
{
storage_account_name => "test2"
storage_access_key => "yyyyyyy"
container => "insights-operational-logs"
codec => "json"
type => "activitylogs"
sincedb => "/usr/share/logstash/data/azure_activity_logs_sincedb"
}
}

**But the Logstash is throwing the following error:**
[2018-08-27T06:09:28,137][ERROR][logstash.inputs.logstashinputazureblob] Unknown setting 'sincedb' for azureblob
[2018-08-27T06:09:28,146][ERROR][logstash.agent ] Failed to execute action {:action=>LogStash::PipelineAction::Create/pipeline_id:main, :exception=>"LogStash::ConfigurationError", :message=>"Something is wrong with your configuration.", :backtrace=>["/usr/share/logstash/logstash-core/lib/logstash/config/mixin.rb:89:in `config_init'", "/usr/share/logstash/logstash-core/lib/logstash/inputs/base.rb:62:in `initialize'", "/usr/share/logstash/logstash-core/lib/logstash/plugins/plugin_factory.rb:97:in `plugin'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:110:in `plugin'", "(eval):8:in `'", "org/jruby/RubyKernel.java:994:in `eval'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:82:in `initialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:167:in `initialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline_action/create.rb:40:in `execute'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:305:in `block in converge_state'"]}

But I did found that **sincedb** is acceptable setting for the azure blob plugin. So what is wrong in my configuration.