fix(unikernels): skip network args in Mewz CommandString when no network

Mewz.CommandString() unconditionally formatted ip=%s/%d and gateway=%s
even when no network was configured, producing "ip=/0 gateway= " as
kernel boot parameters. Mewz does not handle this case and panics.

Guard the network args behind an m.Net.Address != "" check, matching
the existing pattern in Hermit.CommandString(). Add unit tests covering
both the no-network and with-network cases.

Signed-off-by: mdryaan <alikhurshid4u@gmail.com>
Signed-off-by: mdryaan <alikhurshid842001@gmail.com>

Author: mdryaan

pkg/unikontainers/unikernels/mewz.go

@@ -36,8 +36,12 @@ type MewzNet struct {
 }
 
 func (m *Mewz) CommandString() (string, error) {
-	return fmt.Sprintf("ip=%s/%d gateway=%s ", m.Net.Address, m.Net.Mask,
-		m.Net.Gateway), nil
+	var parts []string
+	if m.Net.Address != "" {
+		parts = append(parts, fmt.Sprintf("ip=%s/%d", m.Net.Address, m.Net.Mask))
+		parts = append(parts, fmt.Sprintf("gateway=%s", m.Net.Gateway))
+	}
+	return strings.Join(parts, " "), nil
 }
 
 func (m *Mewz) SupportsBlock() bool {

pkg/unikontainers/unikernels/mewz_test.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2023-2026, Nubificus LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unikernels
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMewzCommandStringNoNetwork(t *testing.T) {
+	t.Parallel()
+	m := &Mewz{}
+	result, err := m.CommandString()
+	require.NoError(t, err)
+	assert.Equal(t, "", result, "CommandString should return empty string when no network is configured")
+}
+
+func TestMewzCommandStringWithNetwork(t *testing.T) {
+	t.Parallel()
+	m := &Mewz{
+		Net: MewzNet{
+			Address: "10.0.0.2",
+			Mask:    24,
+			Gateway: "10.0.0.1",
+		},
+	}
+	result, err := m.CommandString()
+	require.NoError(t, err)
+	assert.Equal(t, "ip=10.0.0.2/24 gateway=10.0.0.1", result)
+}