update asset and setrange with nil checks

pkg/kubecost/asset.go

@@ -3097,6 +3097,9 @@ func (asr *AssetSetRange) IsEmpty() bool {
 }
 
 func (asr *AssetSetRange) MarshalJSON() ([]byte, error) {
+	if asr == nil {
+		return json.Marshal([]*AssetSet{})
+	}
 	asr.RLock()
 	defer asr.RUnlock()
 	return json.Marshal(asr.assets)

pkg/kubecost/asset_test.go

@@ -1424,3 +1424,58 @@ func TestAssetSetRange_Minutes(t *testing.T) {
 		}
 	}
 }
+
+func TestAssetSetRange_MarshalJSON(t *testing.T) {
+
+	tests := []struct {
+		name     string
+		arg      *AssetSetRange
+		expected *AssetSetRange
+	}{
+		{
+			name: "Nil ASR",
+			arg:  nil,
+		},
+		{
+			name: "Nil AS in ASR",
+			arg:  NewAssetSetRange(nil),
+		},
+		{
+			name: "Normal ASR",
+			arg: &AssetSetRange{
+				assets: []*AssetSet{
+					{
+						assets: map[string]Asset{
+							"a": &Any{
+								start: time.Now().UTC().Truncate(day),
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+
+		bytes, err := json.Marshal(test.arg)
+		if err != nil {
+			t.Fatalf("ASR Marshal: test %s, unexpected error: %s", test.name, err)
+		}
+
+		var testASR []*AssetSet
+		marshaled := &testASR
+
+		err = json.Unmarshal(bytes, marshaled)
+
+		if err != nil {
+			t.Fatalf("ASR Unmarshal: test %s: unexpected error: %s", test.name, err)
+		}
+
+		if test.arg.Length() != len(testASR) {
+			t.Fatalf("ASR Unmarshal: test %s: length mutated in encoding: expected %d but got %d", test.name, test.arg.Length(), len(testASR))
+		}
+
+		// asset don't unmarshal back from json
+	}
+}

pkg/kubecost/asset_unmarshal.go

@@ -709,6 +709,9 @@ func (sa *SharedAsset) InterfaceToSharedAsset(itf interface{}) error {
 
 // MarshalJSON JSON-encodes the AssetSet
 func (as *AssetSet) MarshalJSON() ([]byte, error) {
+	if as == nil {
+		return json.Marshal(map[string]Asset{})
+	}
 	as.RLock()
 	defer as.RUnlock()
 	return json.Marshal(as.assets)

pkg/kubecost/etlrange.go

@@ -81,7 +81,7 @@ func (r *SetRange[T]) IsEmpty() bool {
 // MarshalJSON converts SetRange to JSON
 func (r *SetRange[T]) MarshalJSON() ([]byte, error) {
 	if r == nil {
-		return nil, fmt.Errorf("SetRange: MarshalJSON: is nil")
+		return json.Marshal([]T{})
 	}
 	r.lock.RLock()
 	defer r.lock.RUnlock()