message: better error msg for unknown components
diff: @@ -26,6 +26,9 @@ export class MolEncoder extends LigandEncoder {
  const atomMap = this.componentAtomData.entries.get(name)!;
  const bondMap = this.componentBondData.entries.get(name)!;
  + // happens for unknown ligands like UNL
  + if (!atomMap) throw Error(`Component ${name} is not registered in the Chemical Component Dictionary`);
  +
  let bondCount = 0;
  let chiral = false;
  