Can't create sts aws secret roles when using arrays of types/arns despite API returning arrays

[jasonmcintosh]

Trying to use terraform provider "vault generic secret" to manage STS roles in Vault. We had previously created a number of these roles. We upgraded to vault 0.11.4. After upgrading, the vault API returns slightly different json. We've updated our terraform to use that JSON and updates to existing aws secrets work. However, creating a NEW aws secret fails.
API Returns the following on a read:

{
  "credential_types": ["assumed_role"],
  "default_sts_ttl":0,
  "max_sts_ttl":0,
  "policy_arns":null,
  "policy_document":"",
  "role_arns":   ["${aws_iam_role.readonly_role.arn}"]
}

When we try to create this, we get the following:

* max_sts_ttl parameter only valid for assumed_role and federation_token credential types

We're obviously using a assumed_role credential type. What's interesting is this succeeds all day long on a previously created role.

IF we change the above to:

{
  "credential_type": "assumed_role",
  "default_sts_ttl":0,
  "max_sts_ttl":0,
  "policy_arns":null,
  "policy_document":"",
  "role_arn": "${aws_iam_role.readonly_role.arn}"
}

we can create the role, but then the API returns the array based values on every run.

Expected behavior
API should work with either array or non array types and not throw an error when an array type is passed without throwing an error.

Environment:

• Vault Server Version (retrieve with vault status): 0.11.4
• Vault CLI Version (retrieve with vault version): NA
• Server Operating System/Architecture: CentOS 7