GUIStyle in an inspector array

When I use a single GUIStyle in my GameObject, it works : my label is visible. But when I use a GUIStyle array, filled in the inspector, there is no text in my label

First case declaration :

 public GUIStyle myStyle;

First case use :

 GUI.Label(new Rect(0, 0, 100, 30), "Test Label", myStyle);

 

Second case declaration :

 public GUIStyle[] myStyle;

Second case use :

 GUI.Label(new Rect(0, 0, 100, 30), "Test Label", myStyle[0]);

Someone has an explain ?