diff --git a/src/main/java/seedu/address/storage/JsonAdaptedPerson.java b/src/main/java/seedu/address/storage/JsonAdaptedPerson.java
index 9aa028a2b38..2715bf85579 100644
--- a/src/main/java/seedu/address/storage/JsonAdaptedPerson.java
+++ b/src/main/java/seedu/address/storage/JsonAdaptedPerson.java
@@ -141,11 +141,15 @@ public Person toModelType() throws IllegalValueException {
         final Set<Tag> modelTags = new HashSet<>(personTags);
 
         if (type == null) {
-            throw new IllegalValueException(String.format(MISSING_FIELD_MESSAGE_FORMAT, "Type"));
+            throw new IllegalValueException(String.format(MISSING_FIELD_MESSAGE_FORMAT, Type.class.getSimpleName()));
         }
         if (type.equals(TYPE_CLIENT)) {
             return new Client(modelName, modelPhone, modelEmail, modelAddress, modelMeetingTime, modelTags);
         } else if (type.equals(TYPE_LEAD)) {
+            if (keyMilestone == null) {
+                throw new IllegalValueException(String.format(MISSING_FIELD_MESSAGE_FORMAT,
+                        KeyMilestone.class.getSimpleName()));
+            }
             if (!KeyMilestone.isValidKeyMilestone(keyMilestone)) {
                 throw new IllegalValueException(KeyMilestone.MESSAGE_CONSTRAINTS);
             }
diff --git a/src/test/java/seedu/address/storage/JsonAdaptedPersonTest.java b/src/test/java/seedu/address/storage/JsonAdaptedPersonTest.java
index 52cbc429607..d299a2eb143 100644
--- a/src/test/java/seedu/address/storage/JsonAdaptedPersonTest.java
+++ b/src/test/java/seedu/address/storage/JsonAdaptedPersonTest.java
@@ -98,7 +98,6 @@ public void toModelType_nullPhone_throwsIllegalValueException() {
         String expectedMessage = String.format(MISSING_FIELD_MESSAGE_FORMAT, Phone.class.getSimpleName());
         assertThrows(IllegalValueException.class, expectedMessage, person::toModelType);
     }
-    //uncomment later
     @Test
     public void toModelType_nullPhoneWithValidKeyMilestone_throwsIllegalValueException() {
         JsonAdaptedPerson person = new JsonAdaptedPerson(VALID_NAME, null, VALID_EMAIL, VALID_TYPE,
@@ -142,7 +141,6 @@ public void toModelType_nullAddress_throwsIllegalValueException() {
 
     @Test
     public void toModelType_invalidType_throwsIllegalValueException() {
-        //todo: this test need to be fixed, the exception thrown is for meeting type, not for type
         JsonAdaptedPerson person =
                 new JsonAdaptedPerson(VALID_NAME, VALID_PHONE, VALID_EMAIL, INVALID_TYPE, VALID_ADDRESS,
                         CLIENT_KEYMILESTONE_NULL, VALID_MEETING_TIME, VALID_TAGS);
@@ -174,6 +172,7 @@ public void toModelType_leadWithInvalidKeyMilestone_throwsIllegalValueException(
                         VALID_MEETING_TIME, VALID_TAGS);
         assertThrows(IllegalValueException.class, person::toModelType);
     }
+
     @Test
     public void toModelType_invalidTagsWithValidKeyMilestone_throwsIllegalValueException() {
         List<JsonAdaptedTag> invalidTags = new ArrayList<>(VALID_TAGS);
@@ -195,7 +194,6 @@ public void toModelType_invalidMeetingTime_throwsIllegalValueException() {
 
     @Test
     public void toModelType_invalidKeyMilestone_throwsIllegalValueException() {
-        //the meeting time is invalid, need to fix
         JsonAdaptedPerson person =
                 new JsonAdaptedPerson(VALID_NAME, VALID_PHONE, VALID_EMAIL, TYPE_LEAD,
                         VALID_ADDRESS, VALID_KEYMILESTONE, VALID_MEETING_TIME, VALID_TAGS);
@@ -203,10 +201,18 @@ public void toModelType_invalidKeyMilestone_throwsIllegalValueException() {
         assertThrows(IllegalValueException.class, expectedMessage, person::toModelType);
     }
 
+    @Test
+    public void toModelType_nullKeyMilestone_throwsIllegalValueException() {
+        JsonAdaptedPerson person =
+                new JsonAdaptedPerson(VALID_NAME, VALID_PHONE, VALID_EMAIL, TYPE_LEAD,
+                        VALID_ADDRESS, null, VALID_MEETING_TIME, VALID_TAGS);
+        String expectedMessage = String.format(MISSING_FIELD_MESSAGE_FORMAT,
+                KeyMilestone.class.getSimpleName());
+        assertThrows(IllegalValueException.class, expectedMessage, person::toModelType);
+    }
 
     @Test
     public void toModelType_validKeyMilestone_returnsPerson() throws Exception {
-        //the meeting time is invalid, need to fix
         final List<JsonAdaptedTag> validTagBob = BOB.getTags().stream()
                 .map(JsonAdaptedTag::new)
                 .collect(Collectors.toList());