[OTel] Serialize Maps and nil Better (#45042)

This simplifies the serialization of arrays / slices of
`map[string]any`.

Author: pickypg

libbeat/otelbeat/otelmap/otelmap.go

@@ -100,13 +100,11 @@ func ConvertNonPrimitive[T mapstrOrMap](m T) {
 			if ref.Kind() == reflect.Slice || ref.Kind() == reflect.Array {
 				s := make([]any, ref.Len())
 				for i := 0; i < ref.Len(); i++ {
-					elem := ref.Index(i)
-					if elem.Kind() == reflect.Map && elem.Type().Key().Kind() == reflect.String && elem.Type().Elem().Kind() == reflect.Interface {
-						if m, ok := elem.Interface().(map[string]any); ok {
-							ConvertNonPrimitive(m)
-						}
+					elem := ref.Index(i).Interface()
+					if m, ok := elem.(map[string]any); ok {
+						ConvertNonPrimitive(m)
 					}
-					s[i] = elem.Interface()
+					s[i] = elem
 				}
 				m[key] = s
 				break // we figured out the type, so we don't need the unknown type case

libbeat/otelbeat/otelmap/otelmap_test.go

@@ -281,14 +281,18 @@ func TestFromMapstrWithNestedData(t *testing.T) {
 		"bool_slice": []bool{false, true},
 		"inner": []mapstr.M{
 			{
-				"inner_int": 42,
+				"inner_int":       42,
+				"inner_map_slice": [1]any{nil},
 				"inner_slice": []map[string]any{ // slice -> slice
 					{"string": "string"},
 					{"number": 12.3},
 				},
 			},
 			{
 				"inner_int": 43,
+				"inner_map_slice": []any{
+					map[string]any{"string": "string3"},
+				},
 				"inner_slice": [2]map[string]any{ // array -> slice
 					{"string": "string2"},
 					{"number": 12.4},
@@ -303,14 +307,18 @@ func TestFromMapstrWithNestedData(t *testing.T) {
 		"bool_slice": []any{false, true},
 		"inner": []any{
 			map[string]any{
-				"inner_int": 42,
+				"inner_int":       42,
+				"inner_map_slice": []any{nil},
 				"inner_slice": []any{
 					map[string]any{"string": "string"},
 					map[string]any{"number": 12.3},
 				},
 			},
 			map[string]any{
 				"inner_int": 43,
+				"inner_map_slice": []any{
+					map[string]any{"string": "string3"},
+				},
 				"inner_slice": []any{
 					map[string]any{"string": "string2"},
 					map[string]any{"number": 12.4},