fix #3500: crash with `null` completion in lazy lists

Also, add tests for `LazyInitializedList`.

2 files changed, 82 insertions, 0 deletions

diff --git a/main/src/cgeo/geocaching/utils/LazyInitializedList.java b/main/src/cgeo/geocaching/utils/LazyInitializedList.java
index 27649e8..e607919 100644
--- a/main/src/cgeo/geocaching/utils/LazyInitializedList.java
+++ b/main/src/cgeo/geocaching/utils/LazyInitializedList.java
@@ -1,7 +1,10 @@
 package cgeo.geocaching.utils;
 
+import org.eclipse.jdt.annotation.NonNull;
+
 import java.util.AbstractList;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.Callable;
 
@@ -9,6 +12,7 @@ public abstract class LazyInitializedList<ElementType> extends AbstractList<Elem
 
     private volatile List<ElementType> list;
 
+    @NonNull
     private List<ElementType> getList() {
         if (list == null) {
             synchronized(this) {
@@ -20,6 +24,10 @@ public abstract class LazyInitializedList<ElementType> extends AbstractList<Elem
                 } catch (final Exception e) {
                     Log.e("LazyInitializedList.getList", e);
                 }
+                if (list == null) {
+                    Log.e("LazyInitializedList.getList: using an empty list as a fallback");
+                    list = Collections.emptyList();
+                }
             }
         }
         return list;
diff --git a/tests/src/cgeo/geocaching/LazyInitialilzedListTest.java b/tests/src/cgeo/geocaching/LazyInitialilzedListTest.java
new file mode 100644
index 0000000..bc4b6af
--- /dev/null
+++ b/tests/src/cgeo/geocaching/LazyInitialilzedListTest.java
@@ -0,0 +1,74 @@
+package cgeo.geocaching;
+
+import cgeo.geocaching.utils.LazyInitializedList;
+
+import android.test.AndroidTestCase;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class LazyInitialilzedListTest extends AndroidTestCase {
+
+    private static final int MAKE_NULL = -1;
+    private static final int MAKE_EXCEPTION = -2;
+
+    private static class MyList extends LazyInitializedList<Integer> {
+
+        private int counter;
+
+        MyList(int counter) {
+            this.counter = counter;
+        }
+
+        @Override
+        public List<Integer> call() {
+            if (counter == MAKE_NULL) {
+                return null;
+            }
+            if (counter == MAKE_EXCEPTION) {
+                throw new RuntimeException("exception in call()");
+            }
+            final List<Integer> result = new LinkedList<Integer>();
+            for (int i = 0; i < counter; i++) {
+                result.add(counter);
+            }
+            counter += 1;
+            return result;
+        }
+
+        int getCounter() {
+            return counter;
+        }
+
+    }
+
+    public static void testCallOnce() {
+        final MyList l = new MyList(0);
+        assertEquals("call() must not called prematurely", 0, l.getCounter());
+        l.size();
+        assertEquals("call() must be called when needed", 1, l.getCounter());
+        l.size();
+        assertEquals("call() must be called only once", 1, l.getCounter());
+    }
+
+    public static void testSize() {
+        final MyList l = new MyList(3);
+        assertEquals("completed size must be identical to call() result", 3, l.size());
+    }
+
+    public static void testValue() {
+        final MyList l = new MyList(1);
+        assertEquals("value must be identical to call() result", Integer.valueOf(1), l.get(0));
+    }
+
+    public static void testNull() {
+        final MyList l = new MyList(MAKE_NULL);
+        assertEquals("null returned by call() must create an empty list", 0, l.size());
+    }
+
+    public static void testException() {
+        final MyList l = new MyList(MAKE_EXCEPTION);
+        assertEquals("exception in call() must create an empty list", 0, l.size());
+    }
+
+}