Remove potential NPE during first worker replicate request (#652)

Author: jbern0rd

CHANGELOG.md

@@ -31,6 +31,7 @@ All notable changes to this project will be documented in this file.
 - Remove duplicated MongoDB read on `ReplicatesList` during replicate status update. (#647)
 - Use less MongoDB calls when updating a task to a final status. (#649)
 - Save contribution and result updload replicate data when `CONTRIBUTE_AND_FINALIZE_DONE`. (#651)
+- Fix potential `NullPointerException` during first worker replicate request. (#652)
 
 ### Dependency Upgrades
 

src/main/java/com/iexec/core/worker/WorkerService.java

@@ -121,7 +121,8 @@ public boolean isAllowedToJoin(String workerAddress) {
     }
 
     public boolean isWorkerAllowedToAskReplicate(String walletAddress) {
-        Date lastReplicateDemandDate = workerStatsMap.get(walletAddress).getLastReplicateDemandDate();
+        Date lastReplicateDemandDate = workerStatsMap.computeIfAbsent(walletAddress, WorkerStats::new)
+                .getLastReplicateDemandDate();
         if (lastReplicateDemandDate == null) {
             return true;
         }