diff --git a/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java b/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java
index 04e5695800aec007cdd6bb1c30568b27a67ca318..58b70b174d15179e86c60098dcd95fb1d7097b0d 100644
--- a/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java
+++ b/src/main/java/eu/siacs/conversations/services/XmppConnectionService.java
@@ -509,7 +509,8 @@ public class XmppConnectionService extends Service {
         return databaseBackend.isBlockedMedia(cid);
     }
 
-    public boolean isBlockedMediaSha1(final String sha1sum) {
+    public boolean isBlockedMediaSha1(@Nullable final String sha1sum) {
+        if (sha1sum == null) return false;
         try {
             return isBlockedMedia(CryptoHelper.cid(CryptoHelper.hexToBytes(sha1sum), "sha-1"));
         } catch (final NoSuchAlgorithmException e) {