providers/aws: check if instance is set on eip

CHANGELOG.md

@@ -14,6 +14,7 @@ BUG FIXES:
   * core: "~" is expanded in `-var-file` flags. [GH-273]
   * core: Errors with tfvars are shown in console. [GH-269]
   * providers/aws: Refreshing EIP from pre-0.2 state file won't error. [GH-258]
+  * providers/aws: Creating EIP without an instance/network won't fail.
   * providers/digitalocean: Handle situations when resource was destroyed
       manually. [GH-279]
   * providers/digitalocean: Fix a couple scenarios where the diff was

builtin/providers/aws/resource_aws_eip.go

@@ -97,7 +97,7 @@ func resourceAwsEipUpdate(d *schema.ResourceData, meta interface{}) error {
 	domain := resourceAwsEipDomain(d)
 
 	// Only register with an instance if we have one
-	if v := d.Get("instance"); v != nil {
+	if v, ok := d.GetOk("instance"); ok {
 		instanceId := v.(string)
 
 		assocOpts := ec2.AssociateAddress{