Places the string representation of extension value
into the StringBuffer object.
buffer.append(prefix).append("Unparseable extension value:\n"); //$NON-NLS-1$
if (encoding == null) {
encoding = getEncoded();
}
if (encoding == null) {
buffer.append("NULL\n"); //$NON-NLS-1$
} else {
buffer.append(Array.toString(encoding, prefix));
}