Cannot invoke "java.io.Reader.close()" because "reader" is null

This error message indicates that you are trying to call the `close()` method on a `Reader` object that has not been initialized. In other words, the `reader` variable is null, meaning it does not refer to an actual `Reader` object.

To fix this error, you need to ensure that the `reader` variable is properly initialized before calling any methods on it. You can do this by creating a new `Reader` object and assigning it to the `reader` variable, like this:

Reader reader = new FileReader("myfile.txt");

// Use the reader object here

reader.close(); // Make sure to close the reader when you're done with it

Alternatively, you can use a try-with-resources statement to automatically close the `Reader` object when you're done with it, like this:

try (Reader reader = new FileReader("myfile.txt")) {
    // Use the reader object here
}