android support! thanks to TachiWeb devs.

AndroidCompat/src/main/java/com/f2prateek/rx/preferences/StringAdapter.java

@@ -0,0 +1,17 @@
+package com.f2prateek.rx.preferences;
+
+import android.content.SharedPreferences;
+import android.support.annotation.NonNull;
+
+final class StringAdapter implements Preference.Adapter<String> {
+  static final StringAdapter INSTANCE = new StringAdapter();
+
+  @Override public String get(@NonNull String key, @NonNull SharedPreferences preferences) {
+    return preferences.getString(key, null);
+  }
+
+  @Override public void set(@NonNull String key, @NonNull String value,
+      @NonNull SharedPreferences.Editor editor) {
+    editor.putString(key, value);
+  }
+}