Utilities.trim never returns null.

This fixes a crash loop I was seeing on my device and also
preemptively fixes similar NullPointerExceptions.

Bug: 213931730
Test: Manually verified crash loop stopped with this change.
Change-Id: I8d2fc8475d42ac60b7fdc9219421a8c9733c7b9f
(cherry picked from commit 56be73be80)

src/com/android/launcher3/Utilities.java

@@ -460,9 +460,10 @@ public final class Utilities {
      * Trims the string, removing all whitespace at the beginning and end of the string.
      * Non-breaking whitespaces are also removed.
      */
+    @NonNull
     public static String trim(CharSequence s) {
         if (s == null) {
-            return null;
+            return "";
         }
 
         // Just strip any sequence of whitespace or java space characters from the beginning and end