useFieldArray with nested arrays throws error with `append` and `remove` in nested array (data is not iterable)

Describe the bug

Creating a nested useFieldArray

setValue("test", [
  ...(getValues().test || []),
  {
    name: "append",
    nestedArray: [{ field1: "append", field2: "append" }]
  }
]);

does not populate the fields for nestedArray values field1 and field2

Using

remove(k)

to remove the empty nestedArray throws an error. removeAtIndexes - data is not iterable

---

Creating a nested useFieldArray

setValue("test", [
  ...(getValues().test || []),
  {
    name: "append",
    nestedArray: [{ field1: "append", field2: "append" }]
  }
]);

and then using

append({
  field1: "field1",
  field2: "field2"
})

to append a nested array throws an error append - data is not iterable

---

Using

append({ name: "append" });

to create a single level array works.

Using

append({
  field1: "field1",
  field2: "field2"
})

to populate the nestedArray works

Using

setValue("test", [
  ...(getValues().test || []),
  {
    name: "append",
    nestedArray: [{ field1: "append", field2: "append" }]
  }
]);

to create a new nested array clears the values of the other nestedArray

This seems like it could be somewhat related to #5208

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To Reproduce Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/react-hook-form-usefieldarray-nested-arrays-forked-cg4yj?file=/src/index.js
2. Click on ‘Append Nested’ button
3. Notice the fields are not populated with default values
4. Click on ‘Delete Nested’ button
5. Observe thrown error
6. Clear the error and refresh the page
7. Click on ‘Append Nested’ button
8. Click on the new ‘Append Nested’ button that appears above the hr tag
9. Observe error
10. Clear the error and refresh the page
11. Click the ‘Append’ button
12. Click on the new ‘Append Nested’ button that appears above the hr tag
13. Click on the original ‘Append Nested’ button below the hr tag
14. Notice the fields are cleared of their default values

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Codesandbox link (Required) https://codesandbox.io/s/react-hook-form-usefieldarray-nested-arrays-forked-cg4yj?file=/src/index.js

USING v7.6.2

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Expected behavior Should work exactly as the v7.0.0 example without errors

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Desktop (please complete the following information):

• OS: Mac OSX
• Browser: chrome, firefox
• Version 7.6.2

[mason-smith]

@bluebill1049 You rock, thanks for tackling this!

[peakercope]

I’m sorry it was my mistake. I was using prepend to add element with nested array. With setValue it works ok