Fixes Issue 6436: getString(...) must not be null (#6474)

* DatabaseUtils.kt: change getString() to allow null returns

Before this change, a call to getString() would assume that the specified column
name actually exists. A bad String input would cause a null value to be returned
to getString(), which would then throw a NPE because getString() can only return
non null Strings.

This change expands the getString() method to check if the column name exists.
If it does exist, the String is retrieved normally. Else, a null value is
returned. The method signature is changed to allow null return values.

* *Dao.kt: change some usages of getString()

Before this change, the getString() method in DatabaseUtils.kt was changed
to allow returning a null value upon method failure. All usages of getString()
were not changed.

This change updates all usages of getString() which require non null return
values. If null is returned, an empty string is used instead.

---------

Co-authored-by: Nicolas Raoul <nicolas.raoul@gmail.com>

app/src/main/java/fr/free/nrw/commons/bookmarks/items/BookmarkItemsDao.kt

@@ -144,8 +144,18 @@ class BookmarkItemsDao @Inject constructor(
      */
     @SuppressLint("Range")
     fun fromCursor(cursor: Cursor) = with(cursor) {
+        var name = getString(COLUMN_NAME)
+        if (name == null) {
+            name = ""
+        }
+
+        var id = getString(COLUMN_ID)
+        if (id == null) {
+            id = ""
+        }
+
         DepictedItem(
-            getString(COLUMN_NAME),
+            name,
             getString(COLUMN_DESCRIPTION),
             getString(COLUMN_IMAGE),
             getStringArray(COLUMN_INSTANCE_LIST),
@@ -155,7 +165,7 @@ class BookmarkItemsDao @Inject constructor(
                 getStringArray(COLUMN_CATEGORIES_THUMBNAIL_LIST)
             ),
             getString(COLUMN_IS_SELECTED).toBoolean(),
-            getString(COLUMN_ID)
+            id
         )
     }
 

app/src/main/java/fr/free/nrw/commons/bookmarks/pictures/BookmarkPicturesDao.kt

@@ -128,7 +128,10 @@ class BookmarkPicturesDao @Inject constructor(
     }
 
     fun fromCursor(cursor: Cursor): Bookmark {
-        val fileName = cursor.getString(COLUMN_MEDIA_NAME)
+        var fileName = cursor.getString(COLUMN_MEDIA_NAME)
+        if (fileName == null) {
+            fileName = ""
+        }
         return Bookmark(
             fileName, cursor.getString(COLUMN_CREATOR), uriForName(fileName)
         )

app/src/main/java/fr/free/nrw/commons/explore/recentsearches/RecentSearchesDao.kt

@@ -163,11 +163,19 @@ class RecentSearchesDao @Inject constructor(
      * @param cursor
      * @return RecentSearch object
      */
-    fun fromCursor(cursor: Cursor): RecentSearch = RecentSearch(
-        uriForId(cursor.getInt(COLUMN_ID)),
-        cursor.getString(COLUMN_NAME),
-        Date(cursor.getLong(COLUMN_LAST_USED))
-    )
+    fun fromCursor(cursor: Cursor): RecentSearch {
+        var query = cursor.getString(COLUMN_NAME)
+
+        if (query == null) {
+            query = ""
+        }
+
+        return RecentSearch(
+            uriForId(cursor.getInt(COLUMN_ID)),
+            query,
+            Date(cursor.getLong(COLUMN_LAST_USED))
+        )
+    }
 
     /**
      * This class contains the database table architechture for recent searches,

app/src/main/java/fr/free/nrw/commons/utils/DatabaseUtils.kt

@@ -6,9 +6,20 @@ import android.database.Cursor
 fun Cursor.getStringArray(name: String): List<String> =
     stringToArray(getString(name))
 
+/**
+ * Gets the String at the current row and specified column.
+ *
+ * @param name The name of the column to get the String from.
+ * @return The String if the column exists. Else, null is returned.
+ */
 @SuppressLint("Range")
-fun Cursor.getString(name: String): String =
-    getString(getColumnIndex(name))
+fun Cursor.getString(name: String): String? {
+    val index = getColumnIndex(name)
+    if (index == -1) {
+        return null
+    }
+    return getString(index)
+}
 
 @SuppressLint("Range")
 fun Cursor.getInt(name: String): Int =