Preserve null collections in effective YAML

internal/config/load_validate_test.go

@@ -159,15 +159,44 @@ storage:
 }
 
 func TestEffectivePipelineValuesPreserveNilEmptyAndExactIntegers(t *testing.T) {
-	base := &PipelineConfig{Audita: AuditaConfig{Modules: nil}}
+	base := &PipelineConfig{
+		Audita:      AuditaConfig{Modules: nil},
+		Scriptorium: &ScriptoriumConfig{Artifacts: nil},
+		resolution:  &pipelineResolutionMetadata{},
+	}
 	nilValues, err := EffectivePipelineValues(base)
 	if err != nil {
 		t.Fatal(err)
 	}
+	nilYAML, err := MarshalEffectivePipeline(base)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(nilYAML), "modules: null\n") || !strings.Contains(string(nilYAML), "artifacts: null\n") {
+		t.Fatalf("effective YAML lost null collections: %q", nilYAML)
+	}
+	if err := recomputePipelineEffectiveDigest(base); err != nil {
+		t.Fatal(err)
+	}
+	nilDigest := EffectivePipelineDigest(base)
 	base.Audita.Modules = []string{}
-	base.Scriptorium = &ScriptoriumConfig{Artifacts: map[string]ScriptoriumArtifactConfig{
+	base.Scriptorium.Artifacts = map[string]ScriptoriumArtifactConfig{}
+	emptyYAML, err := MarshalEffectivePipeline(base)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(emptyYAML), "modules: []\n") || !strings.Contains(string(emptyYAML), "artifacts: {}\n") {
+		t.Fatalf("effective YAML lost empty collections: %q", emptyYAML)
+	}
+	if err := recomputePipelineEffectiveDigest(base); err != nil {
+		t.Fatal(err)
+	}
+	if emptyDigest := EffectivePipelineDigest(base); emptyDigest == nilDigest {
+		t.Fatalf("null and empty collections have equal digest %q", emptyDigest)
+	}
+	base.Scriptorium.Artifacts = map[string]ScriptoriumArtifactConfig{
 		"recap": {Vars: map[string]any{"exact": int64(9007199254740993)}},
-	}}
+	}
 	emptyValues, err := EffectivePipelineValues(base)
 	if err != nil {
 		t.Fatal(err)