Update public documentation.

Looks like we haven't returned `null` in years.

Fixes: 149837263
Test: None. Documentation only.
Change-Id: I6900458d0b69152a54034e572a6b994e8e6585bd

core/java/android/content/pm/PackageManager.java

@@ -5951,9 +5951,9 @@ public abstract class PackageManager {
     /**
      * Return the label to use for this application.
      *
-     * @return Returns the label associated with this application, or null if
-     * it could not be found for any reason.
-     * @param info The application to get the label of.
+     * @return Returns a {@link CharSequence} containing the label associated with
+     * this application, or its name the  item does not have a label.
+     * @param info The {@link ApplicationInfo} of the application to get the label of.
      */
     @NonNull
     public abstract CharSequence getApplicationLabel(@NonNull ApplicationInfo info);