diff --git a/services/iaas/go.mod b/services/iaas/go.mod
index e0878c3c0..9101515a8 100644
--- a/services/iaas/go.mod
+++ b/services/iaas/go.mod
@@ -1,6 +1,6 @@
 module github.com/stackitcloud/stackit-sdk-go/services/iaas
 
-go 1.21
+go 1.18
 
 require (
 	github.com/google/go-cmp v0.6.0
diff --git a/services/iaas/model_allowed_addresses_inner.go b/services/iaas/model_allowed_addresses_inner.go
index e590b6eb5..d46b83031 100644
--- a/services/iaas/model_allowed_addresses_inner.go
+++ b/services/iaas/model_allowed_addresses_inner.go
@@ -62,7 +62,7 @@ func (src AllowedAddressesInner) MarshalJSON() ([]byte, error) {
 		return json.Marshal(&src.String)
 	}
 
-	return nil, nil // no data in oneOf schemas
+	return []byte("{}"), nil // no data in oneOf schemas => empty JSON object
 }
 
 // Get the actual instance
diff --git a/services/iaas/model_create_protocol.go b/services/iaas/model_create_protocol.go
index 4b0f5b47f..4683d54ab 100644
--- a/services/iaas/model_create_protocol.go
+++ b/services/iaas/model_create_protocol.go
@@ -88,7 +88,7 @@ func (src CreateProtocol) MarshalJSON() ([]byte, error) {
 		return json.Marshal(&src.String)
 	}
 
-	return nil, nil // no data in oneOf schemas
+	return []byte("{}"), nil // no data in oneOf schemas => empty JSON object
 }
 
 // Get the actual instance
diff --git a/services/iaas/model_create_server_payload_networking.go b/services/iaas/model_create_server_payload_networking.go
index 8bebe2e97..965fe1224 100644
--- a/services/iaas/model_create_server_payload_networking.go
+++ b/services/iaas/model_create_server_payload_networking.go
@@ -88,7 +88,7 @@ func (src CreateServerPayloadNetworking) MarshalJSON() ([]byte, error) {
 		return json.Marshal(&src.CreateServerNetworkingWithNics)
 	}
 
-	return nil, nil // no data in oneOf schemas
+	return []byte("{}"), nil // no data in oneOf schemas => empty JSON object
 }
 
 // Get the actual instance