WorkSource: Fix corner-case in equals method.

We should treat WorkSource objects that have a null mChains List
as being equal to one that has an empty non-null mChains List.

This bug was uncovered by the tests added to WifiController in
commit 0068bf953ad25e in frameworks/opt/net/wifi.

Bug: 62390666
Test: WorkSourceTest
Change-Id: Icd1f86aa5178a7beb436621362cfe771a3440398

core/java/android/os/WorkSource.java

@@ -7,7 +7,6 @@ import android.util.proto.ProtoOutputStream;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Objects;
 
 /**
  * Describes the source of some work that may be done by someone else.
@@ -162,9 +161,21 @@ public class WorkSource implements Parcelable {
 
     @Override
     public boolean equals(Object o) {
-        return o instanceof WorkSource
-            && !diff((WorkSource) o)
-            && Objects.equals(mChains, ((WorkSource) o).mChains);
+        if (o instanceof WorkSource) {
+            WorkSource other = (WorkSource) o;
+
+            if (diff(other)) {
+                return false;
+            }
+
+            if (mChains != null && !mChains.isEmpty()) {
+                return mChains.equals(other.mChains);
+            } else {
+                return other.mChains == null || other.mChains.isEmpty();
+            }
+        }
+
+        return false;
     }
 
     @Override

core/tests/coretests/src/android/os/WorkSourceTest.java

@@ -128,6 +128,23 @@ public class WorkSourceTest extends TestCase {
         assertFalse(ws3.equals(ws1));
     }
 
+    public void testEquals_workChains_nullEmptyAreEquivalent() {
+        // Construct a WorkSource that has no WorkChains, but whose workChains list
+        // is non-null.
+        WorkSource ws1 = new WorkSource();
+        ws1.add(100);
+        ws1.createWorkChain().addNode(100, null);
+        ws1.getWorkChains().clear();
+
+        WorkSource ws2 = new WorkSource();
+        ws2.add(100);
+
+        assertEquals(ws1, ws2);
+
+        ws2.createWorkChain().addNode(100, null);
+        assertFalse(ws1.equals(ws2));
+    }
+
     public void testWorkSourceParcelling() {
         WorkSource ws = new WorkSource();