Fix preference crashes

app/proguard.pro

@@ -1,5 +1,7 @@
 -dontobfuscate
 
+-keep class org.tasks.** { *; }
+
 -keep class com.rey.material.widget.Slider
 -dontwarn com.rey.material.**
 

app/src/main/java/org/tasks/injection/InjectingPreferenceFragment.kt

@@ -67,7 +67,10 @@ abstract class InjectingPreferenceFragment : PreferenceFragmentCompat() {
 
     private fun remove(preferenceGroup: PreferenceGroup, resIds: IntArray) {
         for (resId in resIds) {
-            preferenceGroup.removePreference(findPreference(resId))
+            val preference: Preference? = preferenceGroup.findPreference(getString(resId))
+            if (preference != null) {
+                preferenceGroup.removePreference(preference)
+            }
         }
     }
 

app/src/main/res/xml/preferences.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<PreferenceScreen xmlns:app="http://schemas.android.com/apk/res-auto">
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+  xmlns:app="http://schemas.android.com/apk/res-auto">
 
   <Preference
     app:fragment="org.tasks.preferences.fragments.LookAndFeel"
@@ -37,6 +38,7 @@
     app:title="@string/about" />
 
   <Preference
+    android:key="@string/debug"
     app:fragment="org.tasks.preferences.fragments.Debug"
     app:icon="@drawable/ic_outline_bug_report_24px"
     app:title="@string/debug" />