Required rule doesn't work on field if it's nested in object

**Describe the bug**
Required rule doesn't work on the field which is nested inside field of type "object". Builder doesn't show any error message.
This happens only when field is nested inside object. If it's top level field then it works correctly.

**To Reproduce**
Steps to reproduce the behavior:
1. Register custom component with such field definition:
```
inputs: [
{
name: 'someObject',
type: 'object',
subFields: [
{
name: 'someFile',
type: 'file',
required: true,
},
],
},
]
```
2. Put the component in Builder on some page.
3. Check "someFile" field - there is no error message even if there is no file

**Expected behavior**
There should be an error message in the top right corner of Builder editor like "You are missing a required input"

**Screenshots**