add getter and use it; account for the case where a file has no certificates

core/src/main/java/com/muwire/core/SharedFile.java

@@ -109,6 +109,10 @@ public class SharedFile {
         return downloaders;
     }
     
+    public Set<SearchEntry> getSearches() {
+        return searches;
+    }
+    
     public void addDownloader(String name) {
         downloaders.add(name);
     }

gui/griffon-app/models/com/muwire/gui/SharedFileModel.groovy

@@ -19,8 +19,8 @@ class SharedFileModel {
     @Observable boolean showCommentActionEnabled
     
     public void mvcGroupInit(Map<String,String> args) {
-        searchers.addAll(sf.searches)
-        downloaders.addAll(sf.downloaders)
-        certificates.addAll(core.certificateManager.byInfoHash.get(sf.infoHash))
+        searchers.addAll(sf.getSearches())
+        downloaders.addAll(sf.getDownloaders())
+        certificates.addAll(core.certificateManager.byInfoHash.getOrDefault(sf.infoHash,[]))
     }
 }