setBackgroundResource(Drawable) can't accept a selector or shape xml as the parameter?

[pwcat]

For example, a selector file like this:
<?xml version="1.0" encoding="utf-8"?> <selector xmlns:android="http:https://schemas.android.com/apk/res/android"> <item android:drawable="@drawable/et_focused_background" android:state_focused="true"/> <item android:drawable="@drawable/et_unfocus_background" android:state_focused="false"/> </selector>

pass it into the method : editor.setBackgroundResource(R.drawable.post_et_selector)
cause crash:
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.graphics.Bitmap.compress(android.graphics.Bitmap$CompressFormat, int, java.io.OutputStream)' on a null object reference
at jp.wasabeef.richeditor.Utils.toBase64(Utils.java:36)
at jp.wasabeef.richeditor.RichEditor.setBackgroundResource(RichEditor.java:226)

[pwcat]

well, just saw the source codes and understood why. I might need to find another way.