add method to externals implementations for ui modules for description

modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/ExternalUiModule.java

diff --git a/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/ExternalUiModule.java b/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/ExternalUiModule.java
index e835b24..d0f3b5c 100644
--- a/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/ExternalUiModule.java
+++ b/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/ExternalUiModule.java
@@ -137,6 +137,11 @@
     }
 
     @Override
+    public String getDescription() {
+        return null; // not supported here; could be but isn't needed
+    }
+
+    @Override
     public String getIcon() {
         return this.icon;
     }

modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/enricher/BrooklynExternalUiModuleEnricher.java

diff --git a/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/enricher/BrooklynExternalUiModuleEnricher.java b/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/enricher/BrooklynExternalUiModuleEnricher.java
index 9f19f37..9c063a2 100644
--- a/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/enricher/BrooklynExternalUiModuleEnricher.java
+++ b/modularity-server/external-modules/src/main/java/org/apache/brooklyn/ui/modularity/enricher/BrooklynExternalUiModuleEnricher.java
@@ -140,6 +140,12 @@
             }
 
             @Override
+            public String getDescription() {
+                // not supported here (it could be but isn't needed)
+                return null;
+            }
+
+            @Override
             public String getIcon() {
                 return icon;
             }