SchemaEditor: some extra loop protection to enable empty schemas to be loaded.

Author: ddooley

lib/AppContext.js

@@ -399,7 +399,7 @@ export default class AppContext {
     // .inherits[enum1 name, enum2 name, ... , this enum], merging each in order
     // such that permissible value labels, descriptions and mappings can be
     // overwritten.  See https://linkml.io/linkml-model/latest/docs/inherits/ 
-    Object.entries(schema.enums).forEach(([enum_name, enum_obj]) => {
+    Object.entries(schema.enums || {}).forEach(([enum_name, enum_obj]) => {
       if (enum_obj.inherits) {
         const values = {};
         enum_obj.inherits.forEach(inherit_enum_name => {
@@ -1545,7 +1545,7 @@ export default class AppContext {
     });
 
     // For each dependent
-    this.relations[start_name].dependents.keys().forEach((class_name) => {
+    this.relations[start_name]?.dependents?.keys().forEach((class_name) => {
       // 1) Assemble the needed key_vals for this start class and its 
       //    dependents (via foreign keys).
       let [key_vals, fkey_vals, fkey_status] =