fix #23748: NPE: Reverse way direction: Automatic tag correction

(furter already expected regrression from r19101) 
- don't use Map.ofEntries() when map may contain null keys or values

I try to write a unit test for this as well

git-svn-id: https://josm.openstreetmap.de/svn/trunk@19124 0c6e7542-c601-0410-84e7-c038aed88b3b

Author: GerdP

src/org/openstreetmap/josm/tools/Utils.java

@@ -665,8 +665,8 @@ public static <K, V> Map<K, V> toUnmodifiableMap(Map<K, V> map) {
             final Map.Entry<K, V> entry = map.entrySet().iterator().next();
             return Collections.singletonMap(entry.getKey(), entry.getValue());
         }
-        // Map.copyOf would also work, but if the original map is immutable, it just returns the original map.
-        return Map.ofEntries(map.entrySet().toArray(new Map.Entry[0]));
+        // see #23748 don't use Map.ofEntries as it doesn't allow null keys or values
+        return Collections.unmodifiableMap(map);
     }
 
     /**