bugfix: don't use nil state for a computed attribute

[gersonsosa]

Description

If a computed attribute parent state is null, don't try to use the state to avoid inconsistency errors when the apply process finishes the state will still be used in the previous cases to preserve the same functionality.

https://elasticco.atlassian.net/browse/CP-9334

Related Issues

Motivation and Context

We found a bug while fixing the acceptance tests where multiple stateless components have this inconsistent behavior, in the eyes of terraform this is a bug.

The New State object returned from the provider must meet the following constraints:

• Any attribute that had a known value in the Final Planned State must have an identical value in the new state. In particular, if the remote API returned a different serialization of the same value then the provider must preserve the form the user wrote in the configuration, and must not return the normalized form produced by the provider.

See the docs for more details https://github.com/hashicorp/terraform/blob/main/docs/resource-instance-change-lifecycle.md#applyresourcechange

How Has This Been Tested?

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improves code quality but has no user-facing effect)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Readiness Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

[dimuon]

@gersonsosa , the PR looks good besides one comment.

[dimuon]

LGTM