BaseEncoding.encodingStream().close() is non-idempotent

Closeable.close says:

If the stream is already closed then invoking this method has no effect.

Code:

StringWriter w = new StringWriter();
OutputStream out = BaseEncoding.base64().encodingStream(w);
out.write(0);
out.close();
System.out.println(w);
out.close();
System.out.println(w);

Output:

AA==
AA==A===