I can't get my sound to work!

I have been working on a minigolf game, and I want to add a sound for when the player hits the ball, but it won't play the sound and an error keeps popping up:

PlayOneShot was called with a null AudioClip.

Here is my SoundManager script:

using UnityEngine;

public class SoundManager : MonoBehaviour {

 public static AudioClip golfSwingSound;
 static AudioSource audioSrc;

 void Start()
 {

         golfSwingSound = Resources.Load<AudioClip> ("Swing");

         audioSrc = GetComponent<AudioSource> ();
         
 }

     public static void PlaySound (string clip)
     {
         switch (clip) {

             case "Swing":
             audioSrc.PlayOneShot (golfSwingSound);
             break;
         }
     }

}

using UnityEngine;

public class PlayerMovement : MonoBehaviour { void Update { SoundManager.PlaySound ("Swing"); } }

My player movement doesn't look like this, but I think this is all you need. Please let me know if you need the entire player movement script. Also sry I'm new so I don't know how to properly space this stuff.