Make master preview refresh rendertexture on play mode change and check if rendertexture is null

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Inspector/MasterPreviewView.cs

                 middleContainer.AddManipulator(new Scrollable(OnScroll));
             }
             Add(middleContainer);
+
+            EditorApplication.playmodeStateChanged += RefreshRenderTextureSize;
         }
 
         void BuildContextualMenu(ContextualMenuPopulateEvent evt)
 
         public void RefreshRenderTextureSize()
         {
-            RenderTextureDescriptor descriptor = m_PreviewRenderHandle.renderTexture.descriptor;
-
-            if (Mathf.Approximately(descriptor.width, targetHeight) && Mathf.Approximately(descriptor.height, targetWidth))
+            RenderTextureDescriptor descriptor;
+
+            if (m_PreviewRenderHandle.renderTexture)
-                return;
-            }
+                descriptor = m_PreviewRenderHandle.renderTexture.descriptor;
+                descriptor.width = (int)m_PreviewTextureView.contentRect.width;
+                descriptor.height = (int)m_PreviewTextureView.contentRect.height;
-            descriptor.width = (int)m_PreviewTextureView.contentRect.width;
-            descriptor.height = (int)m_PreviewTextureView.contentRect.height;
+                if (Mathf.Approximately(descriptor.width, descriptor.height) && Mathf.Approximately(descriptor.height, descriptor.height))
+                {
+                    return;
+                }
-            m_PreviewRenderHandle.renderTexture.Release();
-            Object.DestroyImmediate(m_PreviewRenderHandle.renderTexture);
-            m_PreviewRenderHandle.renderTexture = new RenderTexture(descriptor);
+                m_PreviewRenderHandle.renderTexture.Release();
+                Object.DestroyImmediate(m_PreviewRenderHandle.renderTexture);
+            }
+            else
+            {
+                descriptor = new RenderTextureDescriptor((int)targetWidth, (int)targetHeight, RenderTextureFormat.ARGB32, 16);
+            }
+            m_PreviewRenderHandle.renderTexture = new RenderTexture(descriptor) { hideFlags = HideFlags.HideAndDontSave };
             DirtyMasterNode(ModificationScope.Node);
         }