fix flag defaults

Author: dcousens

packages/core/src/scripts/cli.ts

@@ -18,7 +18,9 @@ export type Flags = {
 
 function defaultFlags(flags: Partial<Flags>, defaults: Partial<Flags>) {
   for (const [key, value] of Object.entries(flags)) {
-    if (!(key in defaults)) throw new Error(`Option '${key}' is unsupported for this command`);
+    if (value !== undefined && !(key in defaults)) {
+      throw new Error(`Option '${key}' is unsupported for this command`);
+    }
 
     // should we default the flag?
     if (value === undefined) {