java.lang.NullPointerException: storage == null

java.lang.NullPointerException: storage == null
        at java.util.Arrays$ArrayList.<init>(Arrays.java:38)
        at java.util.Arrays.asList(Arrays.java:155)
        at com.github.isabsent.filepicker.SimpleFilePickerDialog.path(SimpleFilePickerDialog.java:326)
        at com.github.isabsent.filepicker.SimpleFilePickerDialog.build(SimpleFilePickerDialog.java:86)

final String rootPath = Environment.getExternalStorageDirectory().getAbsolutePath();
Log.i(TAG, "onCreate: " + rootPath + " --> " + new File(rootPath).canRead());

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=====> onCreate: /storage/sdcard0 --> false

When connecting the device via USB, (in USB storage mode) we have this error ...
External memory is also visible with the 

final String rootPath = Environment.getExternalStorageDirectory().getAbsolutePath();

command.
But not read / write

new File(rootPath).canRead()    - false

new File(rootPath).listFiles()  - null