Fixes for PR

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/ScreenPositionMaterialSlot.cs

     [Serializable]
     public class ScreenPositionMaterialSlot : Vector4MaterialSlot, IMayRequireScreenPosition
     {
+        public ScreenPositionMaterialSlot()
+        {}
+
         public ScreenPositionMaterialSlot(int slotId, string displayName, string shaderOutputName,
                                           ShaderStage shaderStage = ShaderStage.Dynamic, bool hidden = false)
             : base(slotId, displayName, shaderOutputName, SlotType.Input, Vector3.zero, shaderStage, hidden)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Nodes/Input/PBR/DielectricSpecularNode.cs

 
         public void GenerateNodeCode(ShaderGenerator visitor, GenerationMode generationMode)
         {
+            var sb = new ShaderStringBuilder();
+            if (!generationMode.IsPreview())
+            {
+                switch (material.type)
+                {
+                    case DielectricMaterialType.Custom:
+                        sb.AppendLine("{0} _{1}_IOR = {2};", precision, GetVariableNameForNode(), material.indexOfRefraction);
+                        break;
+                    case DielectricMaterialType.Common:
+                        sb.AppendLine("{0} _{1}_Range = {2};", precision, GetVariableNameForNode(), material.range);
+                        break;
+                    default:
+                        break;
+                }
+            }
-                    visitor.AddShaderChunk(string.Format("{0}3 {1} = {0}3(0.030, 0.030, 0.030);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
+                    sb.AppendLine(string.Format("{0}3 {1} = {0}3(0.030, 0.030, 0.030);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
-                    visitor.AddShaderChunk(string.Format("{0}3 {1} = {0}3(0.020, 0.020, 0.020);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
+                    sb.AppendLine(string.Format("{0}3 {1} = {0}3(0.020, 0.020, 0.020);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
-                    visitor.AddShaderChunk(string.Format("{0}3 {1} = {0}3(0.018, 0.018, 0.018);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
+                    sb.AppendLine(string.Format("{0}3 {1} = {0}3(0.018, 0.018, 0.018);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
-                    visitor.AddShaderChunk(string.Format("{0}3 {1} = {0}3(0.040, 0.040, 0.040);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
+                    sb.AppendLine(string.Format("{0}3 {1} = {0}3(0.040, 0.040, 0.040);", precision, GetVariableNameForSlot(kOutputSlotId)), true);
-                    visitor.AddShaderChunk(string.Format("{0}3 {1} = pow({2} - 1, 2) / pow({2} + 1, 2);", precision, GetVariableNameForSlot(kOutputSlotId),
+                    sb.AppendLine(string.Format("{0}3 {1} = pow({2} - 1, 2) / pow({2} + 1, 2);", precision, GetVariableNameForSlot(kOutputSlotId),
-                    visitor.AddShaderChunk(string.Format("{0}3 {1} = lerp(0.034, 0.048, {2});", precision, GetVariableNameForSlot(kOutputSlotId), 
+                    sb.AppendLine(string.Format("{0}3 {1} = lerp(0.034, 0.048, {2});", precision, GetVariableNameForSlot(kOutputSlotId), 
+            visitor.AddShaderChunk(sb.ToString(), false);
         }
 
         public override void CollectPreviewMaterialProperties(List<PreviewProperty> properties)