Fix some nullable warnings.

The `@NonNullByDefault` annotation wasn't working as expected, using a
fork from another team instead. Also added it to the notifications
package where it was missing.

Running null analysis on the code spawned a few warnings, I tried to fix
most / all of them here. Some are benign (the checker has to understand
that a certain variable cannot be null), but some were genuine issues.

Bug: 267476663
Test: atest CtsSafetyCenterTestCases
Change-Id: I992ed765d02c1a7b0a39997ea3718e1de09d4986

2 files changed, 21 insertions, 11 deletions

diff --git a/SafetyCenter/Annotations/java/com/android/safetycenter/annotations/NonNullByDefault.java b/SafetyCenter/Annotations/java/com/android/safetycenter/annotations/NonNullByDefault.java
index d19110652..34b6ce798 100644
--- a/SafetyCenter/Annotations/java/com/android/safetycenter/annotations/NonNullByDefault.java
+++ b/SafetyCenter/Annotations/java/com/android/safetycenter/annotations/NonNullByDefault.java
@@ -15,19 +15,28 @@
  */
 package com.android.safetycenter.annotations;
 
-import androidx.annotation.NonNull;
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PACKAGE;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.CLASS;
 
-import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
 
+import javax.annotation.Nonnull;
 import javax.annotation.meta.TypeQualifierDefault;
 
 /**
- * Annotation to declare all type usages in the annotated instance as {@link NonNull}, unless
- * explicitly marked with a nullable annotation.
+ * Specifies that all type uses are {@link Nonnull} within the annotated package, unless tagged with
+ * {@code @Nullable}. This helps IDEs flag all potential nullability issues without having to use
+ * {@code @NonNull} annotations.
+ *
+ * <p>This is similar to {@code @ParametersAreNonnullByDefault}, but is also applied more widely
+ * (e.g. to methods return types and fields).
  */
-@NonNull
-@TypeQualifierDefault(ElementType.TYPE_USE)
-@Retention(RetentionPolicy.CLASS)
+@Retention(CLASS)
+@Target(PACKAGE)
+@TypeQualifierDefault({PARAMETER, FIELD, METHOD})
+@Nonnull // Android variant cannot be applied as a type qualifier.
 public @interface NonNullByDefault {}
diff --git a/SafetyCenter/ResourcesLib/java/com/android/safetycenter/resources/SafetyCenterResourcesContext.java b/SafetyCenter/ResourcesLib/java/com/android/safetycenter/resources/SafetyCenterResourcesContext.java
index bc56d18ee..5417e7b89 100644
--- a/SafetyCenter/ResourcesLib/java/com/android/safetycenter/resources/SafetyCenterResourcesContext.java
+++ b/SafetyCenter/ResourcesLib/java/com/android/safetycenter/resources/SafetyCenterResourcesContext.java
@@ -290,6 +290,7 @@ public class SafetyCenterResourcesContext extends ContextWrapper {
 
     /** Retrieve assets held in the Safety Center resources APK. */
     @Override
+    @Nullable
     public AssetManager getAssets() {
         if (mAssetsFromApk == null) {
             Context resourcesApkContext = getResourcesApkContext();
@@ -302,6 +303,7 @@ public class SafetyCenterResourcesContext extends ContextWrapper {
 
     /** Retrieve resources held in the Safety Center resources APK. */
     @Override
+    @Nullable
     public Resources getResources() {
         if (mResourcesFromApk == null) {
             Context resourcesApkContext = getResourcesApkContext();
@@ -314,6 +316,7 @@ public class SafetyCenterResourcesContext extends ContextWrapper {
 
     /** Retrieve theme held in the Safety Center resources APK. */
     @Override
+    @Nullable
     public Resources.Theme getTheme() {
         if (mThemeFromApk == null) {
             Context resourcesApkContext = getResourcesApkContext();
@@ -366,9 +369,7 @@ public class SafetyCenterResourcesContext extends ContextWrapper {
         return null;
     }
 
-    /**
-     * Gets a color by resource name
-     */
+    /** Gets a color by resource name */
     @ColorInt
     @Nullable
     public Integer getColorByName(String name) {