Cherry-pick #24760 to 7.x: Fix nil pointer for nil list item

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -44,6 +44,7 @@
 - Fix docker enrollment issue related to Fleet Server change. {pull}24155[24155]
 - Improve log on failure of Endpoint Security installation. {pull}24429[24429]
 - Verify communication to Kibana before updating Fleet client. {pull}24489[24489]
+- Fix nil pointer when null is generated as list item. {issue}23734[23734]
 
 ==== New features
 

x-pack/elastic-agent/pkg/agent/program/testdata/single_config.yml

@@ -40,6 +40,8 @@ inputs:
   use_output: default
   streams:
     - metricset: status
+      processors:
+      - null
       data_stream:
         dataset: docker.status
     - metricset: info

x-pack/elastic-agent/pkg/agent/transpiler/ast.go

@@ -126,7 +126,11 @@ func (d *Dict) Value() interface{} {
 func (d *Dict) Clone() Node {
 	nodes := make([]Node, 0, len(d.value))
 	for _, i := range d.value {
+		if i == nil {
+			continue
+		}
 		nodes = append(nodes, i.Clone())
+
 	}
 	return &Dict{value: nodes}
 }
@@ -350,6 +354,9 @@ func (l *List) Value() interface{} {
 func (l *List) Clone() Node {
 	nodes := make([]Node, 0, len(l.value))
 	for _, i := range l.value {
+		if i == nil {
+			continue
+		}
 		nodes = append(nodes, i.Clone())
 	}
 	return &List{value: nodes}