fix empty json data for class/nft metadata (#332)

modules/nft/types/builder.go

@@ -72,6 +72,10 @@ func (cb ClassBuilder) BuildMetadata(class nft.Class) (string, error) {
 			//when classData is not a legal json, there is no need to parse the data
 			return base64.RawStdEncoding.EncodeToString([]byte(metadata.Data)), nil
 		}
+		//note: if metadata.Data is null, it may cause map to be redefined as nil
+		if kvals == nil {
+			kvals = make(map[string]interface{})
+		}
 	}
 	creator, err := sdk.AccAddressFromBech32(metadata.Creator)
 	if err != nil {
@@ -210,17 +214,21 @@ func (cb ClassBuilder) Build(classID, classURI, classData string) (nft.Class, er
 		}
 	}
 
-	data, err := json.Marshal(dataMap)
-	if err != nil {
-		return nft.Class{}, err
+	var data = ""
+	if len(dataMap) > 0 {
+		dataBz, err := json.Marshal(dataMap)
+		if err != nil {
+			return nft.Class{}, err
+		}
+		data = string(dataBz)
 	}
 
 	any, err := codectypes.NewAnyWithValue(&DenomMetadata{
 		Creator:          creator,
 		Schema:           schema,
 		MintRestricted:   mintRestricted,
 		UpdateRestricted: updateRestricted,
-		Data:             string(data),
+		Data:             data,
 	})
 	if err != nil {
 		return nft.Class{}, err
@@ -261,6 +269,10 @@ func (tb TokenBuilder) BuildMetadata(token nft.NFT) (string, error) {
 			//when nftMetadata is not a legal json, there is no need to parse the data
 			return base64.RawStdEncoding.EncodeToString([]byte(nftMetadata.Data)), nil
 		}
+		//note: if nftMetadata.Data is null, it may cause map to be redefined as nil
+		if kvals == nil {
+			kvals = make(map[string]interface{})
+		}
 	}
 	kvals[TokenKeyName] = MediaField{Value: nftMetadata.Name}
 	kvals[TokenKeyURIhash] = MediaField{Value: token.UriHash}
@@ -317,14 +329,18 @@ func (tb TokenBuilder) Build(classId, tokenId, tokenURI, tokenData string) (nft.
 		}
 	}
 
-	data, err := json.Marshal(dataMap)
-	if err != nil {
-		return nft.NFT{}, err
+	var data = ""
+	if len(dataMap) > 0 {
+		dataBz, err := json.Marshal(dataMap)
+		if err != nil {
+			return nft.NFT{}, err
+		}
+		data = string(dataBz)
 	}
 
 	metadata, err := codectypes.NewAnyWithValue(&NFTMetadata{
 		Name: name,
-		Data: string(data),
+		Data: data,
 	})
 	if err != nil {
 		return nft.NFT{}, err
@@ -338,7 +354,3 @@ func (tb TokenBuilder) Build(classId, tokenId, tokenURI, tokenData string) (nft.
 		Data:    metadata,
 	}, nil
 }
-
-func PopIfExist() {
-
-}

modules/nft/types/builder_test.go

@@ -203,7 +203,7 @@ func TestClassBuilder_Build(t *testing.T) {
 			args: args{
 				classData: `{"irismod:creator":{"value":"f8a9eee6bce5bc043e5feec2baef355f87dbfcdf"},"irismod:description":{"value":"digital cat"},"irismod:mint_restricted":{"value":true},"irismod:name":{"value":"kitty"},"irismod:schema":{"value":"{}"},"irismod:symbol":{"value":"symbol"},"irismod:update_restricted":{"value":true},"irismod:uri_hash":{"value":"uri_hash"}}`,
 			},
-			want:    `{"@type":"/cosmos.nft.v1beta1.Class","id":"cat","name":"kitty","symbol":"symbol","description":"digital cat","uri":"uri","uri_hash":"uri_hash","data":{"@type":"/irismod.nft.DenomMetadata","creator":"cosmos1lz57ae4uuk7qg0jlampt4me4t7rahlxl5pnn3y","schema":"{}","mint_restricted":true,"update_restricted":true,"data":"{}"}}`,
+			want:    `{"@type":"/cosmos.nft.v1beta1.Class","id":"cat","name":"kitty","symbol":"symbol","description":"digital cat","uri":"uri","uri_hash":"uri_hash","data":{"@type":"/irismod.nft.DenomMetadata","creator":"cosmos1lz57ae4uuk7qg0jlampt4me4t7rahlxl5pnn3y","schema":"{}","mint_restricted":true,"update_restricted":true,"data":""}}`,
 			wantErr: false,
 		},
 		{
@@ -240,7 +240,7 @@ func TestClassBuilder_Build(t *testing.T) {
 			require.NoError(t, err, " class cdc.MarshalInterfaceJSON failed")
 
 			if string(got) != tt.want {
-				t.Errorf("ClassBuilder.BuildMetadata() = %v, want %v", got, tt.want)
+				t.Errorf("ClassBuilder.BuildMetadata() = %v, want %v", string(got), tt.want)
 			}
 		})
 	}