fix铸造

(cherry picked from commit b912ab7083de3317b006a17617df56746af91051)

src/main/java/com/izouma/nineth/dto/MintOrderDTO.java

@@ -16,6 +16,8 @@ import javax.persistence.EnumType;
 import javax.persistence.Enumerated;
 import java.math.BigDecimal;
 import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.Optional;
 import java.util.stream.Collectors;
 
 @Data
@@ -89,7 +91,8 @@ public class MintOrderDTO {
         BeanUtils.copyProperties(mintOrder, this);
         this.status = mintOrder.getStatus().getDescription();
         this.consume = mintOrder.isConsume() ? "是" : "否";
-        this.material = mintOrder.getMaterial().stream().map(MintMaterial::getName).collect(Collectors.joining(","));
+        this.material = Optional.ofNullable(mintOrder.getMaterial()).orElse(new ArrayList<>())
+                .stream().map(MintMaterial::getName).collect(Collectors.joining(","));
         this.airDrop = mintOrder.isAirDrop() ? "空投" : "实物";
         this.payMethod = mintOrder.getPayMethod() == null ? "" : mintOrder.getPayMethod().getDescription();
     }