Fixed valueOf: check external only if value is not null

inspector-vc/src/main/java/org/oneedtech/inspect/vc/Assertion.java

@@ -115,11 +115,11 @@ public class Assertion extends Credential {
                         return found;
                     }
                 }
-			}
 
                 // check external type
                 if (validateIri(typeNode)) {
                     return External;
+                }
 			}
 
 			return Unknown;