we can normalize nulls in Read again
we can normalize nulls in Read again

This should be the final change from removing the flatmap normalization.
Since we're no longer trying to a consistent zero or null value in the
flatmap config, rather we're trying to maintain the previously applied
value, ReadResource also needs to apply the normalizeNullValues step in
order to prevent unexpected diffs.

hashicorp/terraform-plugin-sdk,hashicorp/terraform-plugin-sdk