HDRenderPipeline: Update UI of metal mask for LayereLit

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Editor/LitUI.cs

                 }
             }
 
-            m_MaterialEditor.TexturePropertySingleLine((Lit.MaterialId)materialID.floatValue == Lit.MaterialId.LitSpecular ? Styles.maskMapSpecularText : Styles.maskMapSText, maskMap[layerIndex]);
+            m_MaterialEditor.TexturePropertySingleLine((materialID != null && (Lit.MaterialId)materialID.floatValue == Lit.MaterialId.LitSpecular) ? Styles.maskMapSpecularText : Styles.maskMapSText, maskMap[layerIndex]);
 
             m_MaterialEditor.ShaderProperty(normalMapSpace[layerIndex], Styles.normalMapSpaceText);