Fix Terraform crash when creating an entity that already exists (hash…

…icorp#899)

* Fix nil pointer exception

* Add import details to doc

vault/resource_identity_entity.go

@@ -105,6 +105,18 @@ func identityEntityCreate(d *schema.ResourceData, meta interface{}) error {
 	if err != nil {
 		return fmt.Errorf("error writing IdentityEntity to %q: %s", name, err)
 	}
+
+	if resp == nil {
+		path := identityEntityNamePath(name)
+		entityMsg := "Unable to determine entity id."
+
+		if entity, err := client.Logical().Read(path); err == nil {
+			entityMsg = fmt.Sprintf("Entity resource ID %q may be imported.", entity.Data["id"])
+		}
+
+		return fmt.Errorf("Identity Entity %q already exists. %s", name, entityMsg)
+	}
+
 	log.Printf("[DEBUG] Wrote IdentityEntity %q", name)
 
 	d.SetId(resp.Data["id"].(string))

website/docs/r/identity_entity.html.md

@@ -46,3 +46,11 @@ The following arguments are supported:
 ## Attributes Reference
 
 * `id` - The `id` of the created entity.
+
+## Import
+
+Identity entity can be imported using the `id`, e.g.
+
+```
+$ terraform import vault_identity_entity.test "ae6f8ued-0f1a-9f6b-2915-1a2be20dc053"
+```