fix: correct isThing guard

src/core/types/Guards.ts

@@ -24,7 +24,11 @@ import {SCThing, SCThingType} from '../Thing';
  * @param {any} something Something to check
  */
 export function isThing(something: any): something is SCThing {
-  return (something.type && something.type in SCThingType);
+  return (
+    typeof something === 'object'
+    && typeof something.type === 'string'
+    && Object.values(SCThingType).indexOf(something.type) >= 0
+  );
 }
 
 /**