`LogManager.readConfiguration` calls `Properties.load`, which may throw `IllegalArgumentException` if it encounters an invalid unicode escape sequence in the input stream.
In previous versions of the JDK, the IllegalArgumentException was simply propagated to the caller. This was however in violation of the specification, since `LogManager.readConfiguration` is not specified to throw `IllegalArgumentException`. Instead, it is specified to throw `IOException` <i>''if there are problems reading from the stream''</i>.
In Java SE 9, `LogManager.readConfiguration` will no longer propagate such `IllegalArgumentException` directly, but will wrap it inside an `IOException` in order to conform to the specification.