Help with Null Reference Exception please.

I'm getting a Null Reference exception on a line checking if a variable is null before copying it?

ANSWERED

 using UnityEngine;
 using System.Collections.Generic;
 /// <summary>
 /// A simple script that holds an array of audio clips so they can be triggered to play from an animation.
 /// Use PlayClip( clipnumber ) to trigger the clip you would like played.
 /// </summary>
 class Anim_PlayAudio : MonoBehaviour
 {
     /// <summary>
     /// Audio clip and priority data.
     /// </summary>
     [System.Serializable]
     public class Audiodata 
     {
         /// <summary>
         /// A string containing a name for this clip for easy reference in the Inspector;
         /// </summary>
         public string name = "";
         /// <summary>
         /// <see cref="UnityEngine.AudioClip"/>
         /// </summary>
         public AudioClip    audioClip = null;
         /// <summary>
         /// A <see cref="System.Int32"/> specifiying the priority of this AudioClip.
         /// </summary>
         public int            priority = 16;
         public Audiodata() 
         {
             priority = 16;
         }
     }
 
     /// <summary>
     /// An array of <see cref="Anim_PlayAudio.AudioData"/> clips for playback.
     /// </summary>
     public Audiodata[]        audioClips = null;
     private AudioSource[]    _sources = null;
 
     void Awake() 
     {
         if (audioClips == null)
         {
             ZCTDebug.EditorMessageBox( "Anim_PlayAudio on " + this.gameObject.name + ": no Audioclips in list to play. Please add one in the inspector.");
         }
         else 
         {
             _sources = new AudioSource[audioClips.Length];
             for (int i = 0; i < _sources.Length; i++ )
             {
                 _sources[i] = new AudioSource();
                 if (audioClips[i] != null && audioClips[i].audioClip != null) _sources[i].clip = audioClips[i].audioClip;
                 else
                     ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": Audio clip at index " + i + " is null!");
             }
         }
     }
 
     /// <summary>
     /// Plays an audio clip from the audioClips array.
     /// </summary>
     /// <param name="clipNumber">The index of the clip to be played.</param>
     void PlayClip(int clipNumber) 
     {
         if (audioClips == null)
         {
             ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": no Audioclips in list to play. Please add one in the inspector.");
         }
         if (clipNumber >= audioClips.Length)
         {
             ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": Clip selected is out of range. Check your PlayClip( num ) function.");
         }
         if (clipNumber < 0)
         {
             ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": Clip selected is out of range.\n PlayClip( num ) function. Value cannot be less than zero.");
         }
         if (_sources[clipNumber].clip.isReadyToPlay)
         {
             _sources[0].Play();
         }
     }
 
     void PlayClipNamed(string clipDataName)
     {
         if (audioClips == null)
         {
             ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": no Audioclips in list to play.\n Please add one in the inspector.");
         }
         bool _foundclip = false;
         List<int>_indexes = new List<int>();
         for(int i = 0; i < audioClips.Length; i++)
         {
             if ( audioClips[i].audioClip == null) ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": Clip selected does not exist. PlayClip( name ) function. The AudioClip specified is null.");
             if ( audioClips[i].name == clipDataName) _foundclip = true;
             _indexes.Add(i);
         }
 
         if (!_foundclip)
         {
             ZCTDebug.EditorMessageBox("Anim_PlayAudio on " + this.gameObject.name + ": Clip selected does not exist. PlayClip( name ) function. The audio clip specified wasn't found.");
         }
         else
         {
             foreach (int index in _indexes)
             {
                 PlayClip(index);
             }
         }
     }
 }

The line generating the error was:

 if (audioClips[i].audioClip != null) _sources[i].clip = audioClips[i].audioClip;

I'm including the output script referencing this one as well since it's useful to anyone reading this question in the future and in general.

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 
 /// <summary>
 /// Debug replacement for comments only meant to be seen in the Unity Editor console.
 /// </summary>
 public static class ZCTDebug {
     /// <summary>
     /// Output a message to the console after checking to be sure the project is running in the Unity Editor.
     /// </summary>
     /// <param name="Output">A string containing the message to be echoed to the console. Recommended to begin with the name of the outputting Class.</param>
     public static void Log (string Output) {
 
         throw new System.Exception(Output);
     }
 
     /// <summary>
     /// Output a modal popup message box to the editor user.
     /// </summary>
     /// <param name="Output">A string containing the message to be displayed to the user. Recommend including GameObject name and outputting Class name to aid in debugging.</param>
     public static void EditorMessageBox(string Output) 
     {
 #if UNITY_EDITOR
         EditorUtility.DisplayDialog("Error!", Output, "Derp!", "");
 #endif
     }
 }