Dynamic Media upload failed

I am getting below error while running the scene7 workflow 

java.lang.Exception: java.lang.NullPointerException
	at com.day.cq.dam.scene7.internal.impl.Scene7InternalUploadServiceImpl.uploadPost(Scene7InternalUploadServiceImpl.java:430) [com.day.cq.dam.cq-scene7-core:5.12.52]
	at com.day.cq.dam.scene7.impl.process.Scene7UploadProcess.upload(Scene7UploadProcess.java:498) [com.day.cq.dam.cq-scene7-core:5.12.52]
	at com.day.cq.dam.scene7.impl.process.Scene7UploadProcess.execute(Scene7UploadProcess.java:308) [com.day.cq.dam.cq-scene7-core:5.12.52]
	at com.day.cq.workflow.compatibility.CQWorkflowExtProcessProxy.execute(CQWorkflowExtProcessProxy.java:66) [com.day.cq.workflow.cq-workflow-impl:6.3.8]
	at com.adobe.granite.workflow.core.util.WEPProxyHolder.execute(WEPProxyHolder.java:42) [com.adobe.granite.workflow.core:2.0.240]
	at com.adobe.granite.workflow.core.job.ExternalProcessJobHandler.process(ExternalProcessJobHandler.java:144) [com.adobe.granite.workflow.core:2.0.240]
	at org.apache.sling.event.impl.jobs.JobConsumerManager$JobConsumerWrapper.process(JobConsumerManager.java:502) [org.apache.sling.event:4.2.12]
	at org.apache.sling.event.impl.jobs.queues.JobQueueImpl.startJob(JobQueueImpl.java:293) [org.apache.sling.event:4.2.12]
	at org.apache.sling.event.impl.jobs.queues.JobQueueImpl.access$100(JobQueueImpl.java:60) [org.apache.sling.event:4.2.12]
	at org.apache.sling.event.impl.jobs.queues.JobQueueImpl$1.run(JobQueueImpl.java:229) [org.apache.sling.event:4.2.12]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException: null
	at com.day.cq.dam.scene7.impl.utils.RequestUtils.getMimeType(RequestUtils.java:152) [com.day.cq.dam.cq-scene7-core:5.12.52]
	at com.day.cq.dam.scene7.internal.impl.Scene7InternalUploadServiceImpl.uploadPost(Scene7InternalUploadServiceImpl.java:231) [com.day.cq.dam.cq-scene7-core:5.12.52]
	... 12 common frames omitted

it would be great if you can help me sort out  this error