Simple Recursion Method - Accept Integer Parameter N And Return Sum Of First N Reciprocals

I am practicing some basic recursion and I was trying to solve this problem

Write a method sumTo that accepts an integer parameter n and returns the sum of the first n reciprocals. In other words:

sumTo(n) returns: 1 + 1/2 + 1/3 + 1/4 + ... + 1/n

For example, the call of sumTo(2) should return 1.5. The method should return 0.0 if passed the value 0 and should throw an IllegalArgumentException if passed a value less than 0.

This is my attempt to do it , however my output is always a 0.0 , and i do not understand why :

public static double sumTo(int n ){
if(n<0){
throw new IllegalArgumentException();
}
else if (n==0){
return 0.0;

[Code] .....