Close #6421: Download try again should not crash when download does not exist

components/feature/downloads/src/main/java/mozilla/components/feature/downloads/manager/FetchDownloadManager.kt

@@ -76,7 +76,7 @@ class FetchDownloadManager<T : AbstractFetchDownloadService>(
     }
 
     override fun tryAgain(downloadId: Long) {
-        val download = queuedDownloads[downloadId]
+        val download = queuedDownloads[downloadId] ?: return
 
         val intent = Intent(applicationContext, service.java)
         intent.putDownloadExtra(download)

components/feature/downloads/src/test/java/mozilla/components/feature/downloads/manager/FetchDownloadManagerTest.kt

@@ -30,6 +30,7 @@ import org.junit.Test
 import org.junit.runner.RunWith
 import org.mockito.Mockito.verify
 import mozilla.components.feature.downloads.AbstractFetchDownloadService.DownloadJobStatus
+import org.junit.Assert.assertFalse
 import org.mockito.Mockito.times
 
 @RunWith(AndroidJUnit4::class)
@@ -101,6 +102,28 @@ class FetchDownloadManagerTest {
         assertTrue(downloadCompleted)
     }
 
+    @Test
+    fun `try again should not crash when download does not exist`() {
+        val context: Context = mock()
+        downloadManager = FetchDownloadManager(context, MockDownloadService::class, broadcastManager)
+        var downloadCompleted = false
+
+        downloadManager.onDownloadStopped = { _, _, _ -> downloadCompleted = true }
+
+        grantPermissions()
+
+        val id = downloadManager.download(download)!!
+
+        verify(context).startService(any())
+        notifyDownloadCompleted(id)
+        assertTrue(downloadCompleted)
+
+        downloadCompleted = false
+        downloadManager.tryAgain(id + 1)
+        assertFalse(downloadCompleted)
+        verify(context, times(1)).startService(any())
+    }
+
     @Test
     fun `trying to download a file with invalid protocol must NOT triggered a download`() {