Fixing plugin crash when providing empty strings to argument

[sebasslash]

Description

This is a really simple fix that closes #409 by preventing the user to set the names argument for tfe_data_source_workspace_ids to an array of empty strings or an array that contains empty strings. The reason for this is the plugin sdk fetches empty strings as nil values, causing any type casting operations to panic.

There is an alternative up for discussion, let's say the user provides ["wkspace1", "", "wkspace2"], should the plugin read this as ["wkspace1", "wkspace2"] omitting any entries that are nil? This might be a better alternative as [] is a valid assignment and therefore omitting entries that are nil (in a case where all entries are nil) would effectively be the same as [].

Update: Decided to go with the alternative solution

Testing plan

1. In order to test ensure you have your provider overrides setup, and have an available Terraform configuration to test with
2. Create a data source block and apply:

data "tfe_workspace_ids" "this" {
  names = [""],
  organization = "your-org-here"
}

3. You should have a successful apply

To run acceptance test:

TESTARGS="-run TestAccTFEWorkspaceIDsDataSource_namesEmpty" make testacc

[barrettclark]

Can you add this case to the tests? I also noticed there is a test failure, which may just be a flickering test failure.

[sebasslash]

Yeah looks like a flickering test, ran the failed tests locally and they passed.

[brandonc]

That is a new test we should probably keep an eye on it.