Annotate Part Uri as @NonNull

This is in response to automated API feedback.

Change-Id: I6f3c7675dc09bdca6bc30e1b7a8718e46f6ff4b4
Fix: 126699938
Test: Build and existing tests pass
diff --git a/api/current.txt b/api/current.txt
index 4bbae3b..aadf196 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -39397,7 +39397,7 @@
     field public static final String CONTENT_ID = "cid";
     field public static final String CONTENT_LOCATION = "cl";
     field public static final String CONTENT_TYPE = "ct";
-    field public static final android.net.Uri CONTENT_URI;
+    field @NonNull public static final android.net.Uri CONTENT_URI;
     field public static final String CT_START = "ctt_s";
     field public static final String CT_TYPE = "ctt_t";
     field public static final String FILENAME = "fn";
diff --git a/telephony/java/android/provider/Telephony.java b/telephony/java/android/provider/Telephony.java
index 2d8a8cb..ba9ac22 100644
--- a/telephony/java/android/provider/Telephony.java
+++ b/telephony/java/android/provider/Telephony.java
@@ -3039,6 +3039,7 @@
              * The {@code content://} style URL for this table. Can be appended with a part ID to
              * address individual parts.
              */
+            @NonNull
             public static final Uri CONTENT_URI = Uri.withAppendedPath(Mms.CONTENT_URI, "part");
 
             /**