fix bug

mallinkService/src/main/java/com/iformall/service/impl/WxMerchantServiceImpl.java

@@ -923,6 +923,9 @@ public class WxMerchantServiceImpl implements WxMerchantService {
     
     @Override
     public Map<Long,List<WxMerchantVo>> findCouponMerchantVoList(List<Long> couponIds,TenantEntity tenantEntity,boolean hasShop) {
+    	if (null == couponIds || couponIds.size() <= 0) {
+    		return null;
+    	}
 		List<Long> merchantIds = wxCouponMerchantMapper.findMerchantByProductIds(tenantEntity.getTenantId(), couponIds);
 		if(null != merchantIds && merchantIds.size() > 0 ) {
 			WxMerchant merchantQ = new WxMerchant();