Because schema.ResourceDiff can't differentiate between unknown
values and new computed values, unknowns can be lost during an update.
If a planned value converted an unknown to a null, restore the unknown
so that it can be correctly replaced in the final plan.
This folder contains helper libraries for Terraform plugins. A running
joke is that this is "Terraform standard library" for plugins. The goal
of the packages in this directory are to provide high-level helpers to
make it easier to implement the various aspects of writing a plugin for
Terraform.
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