Why do I get a NullPointerException?

I just tried this out of interest:

import java.lang.reflect.Method;

public class MyClass {
    public Method Pow;
    
    public void holePow() throws Exception {
        this.Pow = Math.class.getDeclaredMethod(
            "pow", double.class, double.class);
    }
    
    public static void main(String args[]) throws Exception {
      MyClass hallo = new MyClass();
      hallo.holePow();
      // System.out.println(hallo.Pow(123, 321));
    }
}

The outgoing line at the end does not give the syntax, so you would have to work with invoke(…).