Fixed NullPointerException case on malformed crawl queue folder name

source/net/yacy/cora/protocol/Domains.java

@@ -840,7 +840,7 @@ public class Domains {
      * strip off any parts of an url, address string (containing host/ip:port) or raw IPs/Hosts,
      * considering that the host may also be an (IPv4) IP or a IPv6 IP in brackets.
      * @param target
-     * @return a host name or IP string
+     * @return a domain name or IP string (without square brackets when IPV6)
      */
     public static String stripToHostName(String target) {
         // normalize

source/net/yacy/crawler/HostBalancer.java

@@ -25,6 +25,7 @@ import java.io.IOException;
 import java.lang.reflect.Array;
 import java.net.MalformedURLException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.ConcurrentModificationException;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -543,14 +544,16 @@ public class HostBalancer implements Balancer {
      */
     @Override
     public List<Request> getDomainStackReferences(String host, int maxcount, long maxtime) {
-        if (host == null) return new ArrayList<Request>(0);
+        if (host == null) {
+        	return Collections.emptyList();
+        }
         try {
             HostQueue hq = this.queues.get(DigestURL.hosthash(host, host.startsWith("ftp.") ? 21 : 80));
             if (hq == null) hq = this.queues.get(DigestURL.hosthash(host, 443));
             return hq == null ? new ArrayList<Request>(0) : hq.getDomainStackReferences(host, maxcount, maxtime);
-        } catch (MalformedURLException e) {
+        } catch (final MalformedURLException e) {
             ConcurrentLog.logException(e);
-            return null;
+            return Collections.emptyList();
         }
     }
 

source/net/yacy/crawler/data/NoticedURL.java

@@ -29,6 +29,7 @@ package net.yacy.crawler.data;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -271,9 +272,9 @@ public class NoticedURL {
         switch (stackType) {
             case LOCAL:     return this.coreStack.getDomainStackReferences(host, maxcount, maxtime);
             case GLOBAL:    return this.limitStack.getDomainStackReferences(host, maxcount, maxtime);
-            case REMOTE:   return (this.remoteStack != null) ? this.remoteStack.getDomainStackReferences(host, maxcount, maxtime) : null;
+            case REMOTE:   return (this.remoteStack != null) ? this.remoteStack.getDomainStackReferences(host, maxcount, maxtime) : Collections.emptyList();
             case NOLOAD:   return this.noloadStack.getDomainStackReferences(host, maxcount, maxtime);
-            default: return null;
+            default: return Collections.emptyList();
         }
     }