diff --git a/build.gradle b/build.gradle
index 5d53800..540d704 100644
--- a/build.gradle
+++ b/build.gradle
@@ -6,7 +6,7 @@ plugins {
 
 java {
     group = 'eu.openaire.urls_controller'
-    version = '2.8.0'
+    version = '2.8.1-SNAPSHOT'
     sourceCompatibility = JavaVersion.VERSION_1_8
 }
 
diff --git a/src/main/java/eu/openaire/urls_controller/models/BulkImportReport.java b/src/main/java/eu/openaire/urls_controller/models/BulkImportReport.java
index ccc80d8..b9b8d0e 100644
--- a/src/main/java/eu/openaire/urls_controller/models/BulkImportReport.java
+++ b/src/main/java/eu/openaire/urls_controller/models/BulkImportReport.java
@@ -34,12 +34,12 @@ public class BulkImportReport {
     private String reportID;
 
     // This will not be serialized, since Gson cannot serialize Multimaps. Instead, it will be converted to the "simpler" map below.
-    transient private SetMultimap<String, String> eventsMultimap = Multimaps.synchronizedSetMultimap(LinkedHashMultimap.create());
+    transient private SetMultimap<String, String> eventsMultimap = LinkedHashMultimap.create();
     // We need a "LinkedHashMultimap", se that the order of the keys (timestamps) stay ascending, so the final report makes sense in chronological order.
     // We need for one key (timestamp) to have multiple values (events), in order to not lose events happening at the same time.
 
     @JsonProperty
-    private Map<String, Collection<String>> eventsMap;
+    private Map<String, Collection<String>> eventsMap = null;
 
     transient private final Lock reportLock = new ReentrantLock(true);
 
@@ -52,7 +52,9 @@ public class BulkImportReport {
 
 
     public void addEvent(String event) {
+        reportLock.lock();
         eventsMultimap.put(GenericUtils.getReadableCurrentTimeAndZone(), event);    // This is synchronized.
+        reportLock.unlock();
     }
 
     /**