Made nic_type expansion expect a string (#4598) (#3060)

Related to GoogleCloudPlatform/terraform-validator#195

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/4598.txt

@@ -0,0 +1,3 @@
+```release-note:none
+
+```

google-beta/compute_instance_helpers.go

@@ -250,19 +250,12 @@ func expandNetworkInterfaces(d TerraformResourceData, config *Config) ([]*comput
 			Subnetwork:    sf.RelativeLink(),
 			AccessConfigs: expandAccessConfigs(data["access_config"].([]interface{})),
 			AliasIpRanges: expandAliasIpRanges(data["alias_ip_range"].([]interface{})),
-			NicType:       expandNicType(data["nic_type"].(interface{})),
+			NicType:       data["nic_type"].(string),
 		}
 	}
 	return ifaces, nil
 }
 
-func expandNicType(d interface{}) string {
-	if d == nil {
-		return ""
-	}
-	return d.(string)
-}
-
 func flattenServiceAccounts(serviceAccounts []*computeBeta.ServiceAccount) []map[string]interface{} {
 	result := make([]map[string]interface{}, len(serviceAccounts))
 	for i, serviceAccount := range serviceAccounts {