Index: /trunk/src/org/openstreetmap/josm/gui/tagging/TaggingPreset.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/tagging/TaggingPreset.java	(revision 5794)
+++ /trunk/src/org/openstreetmap/josm/gui/tagging/TaggingPreset.java	(revision 5795)
@@ -1332,4 +1332,11 @@
             return Collections.singleton(value);
         }
+
+        @Override
+        public String toString() {
+            return "Key [key=" + key + ", value=" + value + ", text=" + text
+                    + ", text_context=" + text_context + ", match=" + match
+                    + "]";
+        }
     }
 
@@ -1543,4 +1550,8 @@
                         if (o instanceof ComboMultiSelect) {
                             ((ComboMultiSelect) o).addListEntries(listEntries);
+                        } else if (o instanceof Key) {
+                            if (((Key) o).value == null) {
+                                ((Key) o).value = ""; // Fix #8530
+                            }
                         }
                         listEntries = new LinkedList<PresetListEntry>();