diff --git a/arduino-core/src/cc/arduino/libraries/contributions/ContributedLibrary.java b/arduino-core/src/cc/arduino/libraries/contributions/ContributedLibrary.java
index 255338bb1..d5daf22b1 100644
--- a/arduino-core/src/cc/arduino/libraries/contributions/ContributedLibrary.java
+++ b/arduino-core/src/cc/arduino/libraries/contributions/ContributedLibrary.java
@@ -47,6 +47,8 @@ public abstract class ContributedLibrary extends DownloadableContribution {
 
   public abstract String getCategory();
 
+  public abstract void setCategory(String category);
+
   public abstract String getLicense();
 
   public abstract String getParagraph();
@@ -79,7 +81,7 @@ public abstract class ContributedLibrary extends DownloadableContribution {
   /**
    * Returns <b>true</b> if the library declares to support the specified
    * architecture (through the "architectures" property field).
-   * 
+   *
    * @param reqArch
    * @return
    */
@@ -91,7 +93,7 @@ public abstract class ContributedLibrary extends DownloadableContribution {
   /**
    * Returns <b>true</b> if the library declares to support at least one of the
    * specified architectures.
-   * 
+   *
    * @param reqArchs
    *          A List of architectures to check
    * @return
diff --git a/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndex.java b/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndex.java
index 10fd5bbe9..349d6088d 100644
--- a/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndex.java
+++ b/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndex.java
@@ -28,9 +28,7 @@
  */
 package cc.arduino.libraries.contributions;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
+import java.util.*;
 
 public abstract class LibrariesIndex {
 
@@ -46,24 +44,22 @@ public abstract class LibrariesIndex {
 
   @Override
   public String toString() {
-    String res = "";
-    for (ContributedLibrary l : getLibraries())
-      res += l.toString();
-    return res;
+    StringBuilder sb = new StringBuilder();
+    for (ContributedLibrary library : getLibraries()) {
+      sb.append(library.toString());
+    }
+    return sb.toString();
   }
 
-  private List<String> categories = new ArrayList<String>();
-
   public List<String> getCategories() {
-    return categories;
-  }
-
-  public void fillCategories() {
-    categories.clear();
+    List<String> categories = new LinkedList<String>();
     for (ContributedLibrary lib : getLibraries()) {
-      if (!categories.contains(lib.getCategory()))
+      if (lib.getCategory() != null && !categories.contains(lib.getCategory())) {
         categories.add(lib.getCategory());
+      }
     }
     Collections.sort(categories);
+
+    return categories;
   }
 }
diff --git a/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndexer.java b/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndexer.java
index 96cc38c15..109bd332d 100644
--- a/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndexer.java
+++ b/arduino-core/src/cc/arduino/libraries/contributions/LibrariesIndexer.java
@@ -64,15 +64,12 @@ public class LibrariesIndexer {
         "libraries");
   }
 
-  public void parseIndex() throws JsonParseException, IOException {
+  public void parseIndex() throws IOException {
     parseIndex(indexFile);
-
-    index.fillCategories();
     // TODO: resolve libraries inner references
   }
 
-  private void parseIndex(File indexFile) throws JsonParseException,
-      IOException {
+  private void parseIndex(File indexFile) throws IOException {
     InputStream indexIn = new FileInputStream(indexFile);
     ObjectMapper mapper = new ObjectMapper();
     mapper.registerModule(new MrBeanModule());
@@ -80,6 +77,12 @@ public class LibrariesIndexer {
     mapper.configure(DeserializationFeature.EAGER_DESERIALIZER_FETCH, true);
     mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, true);
     index = mapper.readValue(indexIn, LibrariesIndex.class);
+
+    for (ContributedLibrary library : index.getLibraries()) {
+      if (library.getCategory() == null || "".equals(library.getCategory())) {
+        library.setCategory("Uncategorized");
+      }
+    }
   }
 
   public void setLibrariesFolders(List<File> _librariesFolders)
@@ -172,7 +175,7 @@ public class LibrariesIndexer {
    * Set the sketchbook library folder. <br />
    * New libraries will be installed here. <br />
    * Libraries not found on this folder will be marked as read-only.
-   * 
+   *
    * @param folder
    */
   public void setSketchbookLibrariesFolder(File folder) {
diff --git a/arduino-core/src/processing/app/packages/LegacyUserLibrary.java b/arduino-core/src/processing/app/packages/LegacyUserLibrary.java
index 34f09ef9c..0bed82589 100644
--- a/arduino-core/src/processing/app/packages/LegacyUserLibrary.java
+++ b/arduino-core/src/processing/app/packages/LegacyUserLibrary.java
@@ -80,7 +80,7 @@ public class LegacyUserLibrary extends UserLibrary {
 
   @Override
   public String getCategory() {
-    return null;
+    return "Uncategorized";
   }
 
   @Override
diff --git a/arduino-core/src/processing/app/packages/UserLibrary.java b/arduino-core/src/processing/app/packages/UserLibrary.java
index f92cd0087..10bffe047 100644
--- a/arduino-core/src/processing/app/packages/UserLibrary.java
+++ b/arduino-core/src/processing/app/packages/UserLibrary.java
@@ -199,6 +199,11 @@ public class UserLibrary extends ContributedLibrary {
     return CATEGORIES;
   }
 
+  @Override
+  public void setCategory(String category) {
+    this.category = category;
+  }
+
   @Override
   public String getVersion() {
     return version;