Use Node literal in MergeNode, not EmptyNode()

EmptyNode populates empty sub-structs, which interferes with omitempty during
serialization.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

overlays/debug/internal/debug_test.go

@@ -85,9 +85,11 @@ data from other structures.
 - Discoverable: 
 - Profiles: default
 - Tags: 
+
 - Kernel:
   - Version: 
   - Args: quiet crashkernel=no vga=791 net.naming-scheme=v238
+
 - Ipmi:
   - UserName: user
   - Password: password
@@ -195,9 +197,11 @@ data from other structures.
   - AssetKey: 
   - Profiles: [default]
   - Tags: 
+
   - Kernel
     - Version: 
     - Args: quiet crashkernel=no vga=791 net.naming-scheme=v238
+
   - Ipmi:
     - Ipaddr: 192.168.4.21
     - Netmask: 255.255.255.0
@@ -250,19 +254,11 @@ data from other structures.
   - AssetKey: 
   - Profiles: [default]
   - Tags: 
+
   - Kernel
     - Version: 
     - Args: quiet crashkernel=no vga=791 net.naming-scheme=v238
-  - Ipmi:
-    - Ipaddr: <nil>
-    - Netmask: <nil>
-    - Port: 
-    - Gateway: <nil>
-    - UserName: 
-    - Password: 
-    - Interface: 
-    - Write: 
-    - Tags: 
+
   - NetDevs[default]:
     - Type: 
     - OnBoot: true

overlays/debug/rootfs/warewulf/template-variables.md.ww

@@ -27,9 +27,12 @@ data from other structures.
 - Discoverable: {{ .Discoverable }}
 - Profiles: {{ range $index, $value := .Profiles }}{{ if $index }},{{ end }}{{ $value }}{{ end }}
 - Tags: {{ range $key, $value := .Tags }}{{ $key }}={{ $value }} {{ end }}
+{{ if .Kernel }}
 - Kernel:
   - Version: {{ .Kernel.Version }}
   - Args: {{ .Kernel.Args }}
+{{- end }}
+{{ if .Ipmi }}
 - Ipmi:
   - UserName: {{ .Ipmi.UserName }}
   - Password: {{ .Ipmi.Password }}
@@ -40,6 +43,7 @@ data from other structures.
   - Interface: {{ .Ipmi.Interface }}
   - Write: {{ .Ipmi.Write }}
   - Tags: {{ range $key, $value := .Ipmi.Tags }}{{ $key }}={{ $value }} {{ end }}
+{{- end }}
 {{- range $index, $netdev := .NetDevs }}
 - NetDevs[{{ $index }}]:
   - Type: {{ $netdev.Type }}
@@ -136,9 +140,12 @@ data from other structures.
   - AssetKey: {{ $node.AssetKey }}
   - Profiles: {{ $node.Profiles }}
   - Tags: {{ range $key, $value := $node.Tags }}{{ $key }}={{ $value }} {{ end }}
+{{ if .Kernel }}
   - Kernel
     - Version: {{ $node.Kernel.Version }}
     - Args: {{ $node.Kernel.Args }}
+{{- end }}
+{{ if .Ipmi }}
   - Ipmi:
     - Ipaddr: {{ $node.Ipmi.Ipaddr }}
     - Netmask: {{ $node.Ipmi.Netmask }}
@@ -149,6 +156,7 @@ data from other structures.
     - Interface: {{ $node.Ipmi.Interface }}
     - Write: {{ $node.Ipmi.Write }}
     - Tags: {{ range $key, $value := $node.Ipmi.Tags }}{{ $key }}={{ $value }} {{ end }}
+{{- end }}
 {{- range $index, $netdev := $node.NetDevs }}
   - NetDevs[{{ $index }}]:
     - Type: {{ $netdev.Type }}