Mule flow is not triggering - mule

Question

I am using Groovy inside Poll to check file existence at given location.
My flow is working fine, when there is a file. But If I delete that file, flow is not triggering.Below is my code
<flow name="monitor-dst-file-flow">
<poll doc:name="Poll">
<schedulers:cron-scheduler expression="0 0 23 ? * TUE-SAT"/>
<scripting:transformer doc:name="Groovy">
<scripting:script engine="Groovy"><![CDATA[def endpointBuilder = muleContext.endpointFactory.getEndpointBuilder(
"sftp://${user}:${pwForGroovy}#${host}:${port}${inputpath}/?connector=SFTP")
endpointBuilder.addMessageProcessor(new org.mule.routing.MessageFilter(new org.mule.transport.file.filters.FilenameWildcardFilter('test.txt')))
def inboundEndpoint = endpointBuilder.buildInboundEndpoint()
inboundEndpoint.request(30000L)]]>
</scripting:transformer>
</poll>
<choice doc:name="Choice">
<when expression="#[message.inboundProperties.originalFilename =="test.txt"]">
<logger level="INFO" doc:name="Logger" message="File Exists..."/>
</when>
<otherwise>
<logger message="FILE EXISTS" level="ERROR" doc:name="Logger"/>
<flow-ref name="email-notification-sub-flow" doc:name="Flow Reference"/>
</otherwise>
</choice>
</flow>
Here, if there is no test.txt file, I am not able to debug Choice component.
It says -Polling of monitor-dst-file-flow returned null, the flow will not be invoked.
I am not able to identify the exact solution to run my flow. I have to handle that condition, where given file is not there.

Answer 1

You need to return something besides null from the poller's target for the flow to be invoked. I'd recommend doing this in a sub-flow:
<flow name="monitor-dst-file-flow">
<poll doc:name="Poll">
<schedulers:cron-scheduler expression="0 0 23 ? * TUE-SAT"/>
<flow-ref name="pollerProcessor" doc:name="pollerProcessor"/>
</poll>
<choice doc:name="Choice">
<when expression="#[payload == 'file not found']">
<logger level="INFO" doc:name="Logger" message="File Exists..."/>
</when>
<otherwise>
<logger message="FILE EXISTS" level="ERROR" doc:name="Logger"/>
<flow-ref name="email-notification-sub-flow" doc:name="Flow Reference"/>
</otherwise>
</choice>
</flow>
<sub-flow name="pollerProcessor">
<scripting:transformer doc:name="Groovy">
<scripting:script engine="Groovy"><![CDATA[def endpointBuilder = muleContext.endpointFactory.getEndpointBuilder(
"sftp://${user}:${pwForGroovy}#${host}:${port}${inputpath}/?connector=SFTP")
endpointBuilder.addMessageProcessor(new org.mule.routing.MessageFilter(new org.mule.transport.file.filters.FilenameWildcardFilter('test.txt')))
def inboundEndpoint = endpointBuilder.buildInboundEndpoint() inboundEndpoint.request(30000L)]]>
</scripting:script>
</scripting:transformer>
<set-payload value="#[payload == null ? 'file not found' : payload]" doc:name="Set Payload"/>
</sub-flow>