I made this small snippet to demonstrate this problem:
public static void main(final String[] args) {
    final char[] buffer = new char[100];
    try {
        final FileReader reader = new FileReader("test.txt");
        reader.read(buffer);
        reader.close();
    } catch (IOException exception) {
        exception.printStackTrace();
    }
}

When I use "Convert to try-with-resources", I get:
public static void main(final String[] args) {
    final char[] buffer = new char[100];
    try {
        try (FileReader reader = new FileReader("test.txt")) {
            reader.read(buffer);
        }
    } catch (IOException exception) {
        exception.printStackTrace();
    }
}

I don't see why it created a nested try-with-resources block instead of adding the resources to the existing try block, like this:
public static void main(final String[] args) {
    final char[] buffer = new char[100];
    try (FileReader reader = new FileReader("test.txt")) {
        reader.read(buffer);
    } catch (IOException exception) {
        exception.printStackTrace();
    }
}