fix(proxy-state-tree): fix error where undefined is returned from function

Author: christianalfoni

packages/node_modules/proxy-state-tree/src/proxify.ts

@@ -130,7 +130,7 @@ function createObjectProxy(tree, value, path) {
           ? tree.options.dynamicWrapper(tree, nestedPath, targetValue)
           : targetValue(tree, nestedPath)
 
-        if (dynamicValue[IS_PROXY]) {
+        if (dynamicValue && dynamicValue[IS_PROXY]) {
           delete dynamicValue[VALUE][tree.PROXY]
           Object.defineProperty(dynamicValue[VALUE], tree.PROXY, {
             configurable: true,