fix: return None if substructure data is not set

src/component/component.js

@@ -128,7 +128,7 @@ class pdbLigandEnv extends LitElement {
   }
 
   set highlightColor(data) {
-    if (!data || !this.display) return;
+    if (!data || !this.display || !this.substructureHighlight) return;
 
     this.highlightColor = data;
     this.display.addLigandHighlight(this.substructureHighlight, this.highlightColor);