diff --git a/src/main/java/com/kimgo/wepush/controller/CallerController.java b/src/main/java/com/kimgo/wepush/controller/CallerController.java
index 39f4a57..f4079e0 100644
--- a/src/main/java/com/kimgo/wepush/controller/CallerController.java
+++ b/src/main/java/com/kimgo/wepush/controller/CallerController.java
@@ -20,14 +20,18 @@ public class CallerController {
     public ServerResponseEntity receiveCall(@RequestHeader("accessToken") String accessToken,
                                             @RequestBody @Valid CallInfo callInfo) {
         logger.info("CallInfoO: {}",callInfo.toString());
-        if(accessToken == null || callInfo == null){
+        if(accessToken == null){
             return ServerResponseEntity.fail("accessToken cannot be empty.");
         }
-        if(callInfo.getPhoneNumber().equals("null") || callInfo.getCallTime().equals("null")){
-            logger.info("CallInfo has null String.");
+        if (callInfo == null || isNullOrEmptyOrLiteralNull(callInfo.getPhoneNumber()) ||
+                isNullOrEmptyOrLiteralNull(callInfo.getCallTime())) {
+            logger.info("CallInfo has invalid fields.");
             return ServerResponseEntity.fail("json body value error.");
         }
         return callService.getPhoneNumber(accessToken,callInfo);
     }
+    private boolean isNullOrEmptyOrLiteralNull(String value) {
+        return value == null || value.isEmpty() || "null".equals(value);
+    }
 }