Index: trunk/src/org/openstreetmap/josm/io/protocols/data/Handler.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/protocols/data/Handler.java	(revision 13649)
+++ trunk/src/org/openstreetmap/josm/io/protocols/data/Handler.java	(revision 13650)
@@ -6,4 +6,5 @@
 import java.net.URLConnection;
 import java.net.URLStreamHandler;
+import java.util.Optional;
 
 import org.openstreetmap.josm.tools.Utils;
@@ -31,6 +32,6 @@
 
         String protocolHandlers = Utils.getSystemProperty("java.protocol.handler.pkgs");
-        if (protocolHandlers != null && !protocolHandlers.contains(pkg)) {
-            StringBuilder sb = new StringBuilder(protocolHandlers);
+        if (protocolHandlers == null || !protocolHandlers.contains(pkg)) {
+            StringBuilder sb = new StringBuilder(Optional.ofNullable(protocolHandlers).orElse(""));
             if (sb.length() > 0) {
                 sb.append('|');