diff --git a/src/main/java/org/gcube/contentmanagement/blobstorage/transport/TransportManagerFactory.java b/src/main/java/org/gcube/contentmanagement/blobstorage/transport/TransportManagerFactory.java
index 30825dd..dffd142 100644
--- a/src/main/java/org/gcube/contentmanagement/blobstorage/transport/TransportManagerFactory.java
+++ b/src/main/java/org/gcube/contentmanagement/blobstorage/transport/TransportManagerFactory.java
@@ -48,13 +48,13 @@ public class TransportManagerFactory {
 			logger.debug("transportLayer with "+transport.memoryType+" already instatiated. New memoryType request is "+memoryType);
 // if we haven't any transport layer instantiated or the transport layer is istantiated on another memory type (persistent, volatile), 
 // then a new transport layer is needed		
-		if(Objects.isNull(transport) || (!transport.memoryType.equals(memoryType))) {
+		if(Objects.isNull(tm) || Objects.isNull(tm.memoryType) || (!tm.memoryType.equals(memoryType))) {
 			logger.info("new transport layer instantiated for "+memoryType+" memory");
 			return load(backendType, memoryType, dbNames, writeConcern, readConcern);
 		}else {
 			logger.debug("new transport layer not instantiated.");
 		}
-		return transport;
+		return tm;
 	}
 	
 	private TransportManager  load(String backendType, MemoryType memoryType, String[] dbNames, String writeConcern, String readConcern){