message: type assertion
diff: @@ -15,6 +15,7 @@ import { PluginContext } from '../../mol-plugin/context';
  import { Assembly, Symmetry } from '../../mol-model/structure/model/properties/symmetry';
  import { PluginStateObject as SO } from '../objects';
  import { ModelSymmetry } from '../../mol-model-formats/structure/property/symmetry';
  +import { assertUnreachable } from '../../mol-util/type-helpers';
  const CommonStructureParams = {
  dynamicBonds: PD.Optional(PD.Boolean(false, { description: 'Ensure bonds are recalculated upon model changes. Also enables calculation of inter-unit bonds in water molecules and ions.' })),
  @@ -188,6 +189,6 @@ export namespace RootStructureDefinition {
  return buildSymmetryAssembly(ctx, model, params.params.generators, symmetry, props);
  }
  - throw new Error(`Unknown represetation type: ${(params as any).name}`);
  + assertUnreachable(params);
  }
  }
  \ No newline at end of file
  