Enable nullability in Content.Server (#3685)

Content.Server/GameObjects/Components/Construction/ComputerBoardComponent.cs

@@ -1,6 +1,4 @@
 using Robust.Shared.GameObjects;
-using Robust.Shared.Prototypes;
-using Robust.Shared.Serialization;
 using Robust.Shared.Serialization.Manager.Attributes;
 using Robust.Shared.ViewVariables;
 
@@ -13,6 +11,6 @@ namespace Content.Server.GameObjects.Components.Construction
 
         [ViewVariables]
         [DataField("prototype")]
-        public string Prototype { get; private set; }
+        public string? Prototype { get; private set; }
     }
 }