diff --git a/services/GithubService.js b/services/GithubService.js
index 8cfac87..6023d4f 100644
--- a/services/GithubService.js
+++ b/services/GithubService.js
@@ -221,7 +221,7 @@ async function getUserIdByLogin(copilot, login) {
   Joi.attempt({copilot, login}, getUserIdByLogin.schema);
   const github = await _authenticate(copilot.accessToken);
   const user = await github.users.getForUser({username: login});
-  return user.length ? user.id : null;
+  return user.data ? user.data.id : null;
 }
 
 getUserIdByLogin.schema = {
diff --git a/services/IssueService.js b/services/IssueService.js
index 1381529..ce3fc46 100755
--- a/services/IssueService.js
+++ b/services/IssueService.js
@@ -211,6 +211,12 @@ async function handleIssueAssignment(event, issue, force = false) {
         return;
       }
 
+      // The issue has registered assignee. Ignore it.
+      // If there is assignee changes, it will be handled at handleIssueUnassignment and this func will be called again.
+      if (dbIssue.assignee) {
+        return;
+      }
+
       // ensure issue has open for pickup label
       const hasOpenForPickupLabel = _(issue.labels).includes(config.OPEN_FOR_PICKUP_ISSUE_LABEL); // eslint-disable-line lodash/chaining
       const hasNotReadyLabel = _(issue.labels).includes(config.NOT_READY_ISSUE_LABEL); // eslint-disable-line lodash/chaining
@@ -670,7 +676,7 @@ async function handleIssueUnAssignment(event, issue) {
     }
 
     if (dbIssue.assignee) {
-      const assigneeUserId = gitHelper.getUserIdByLogin(event, dbIssue.assignee);
+      const assigneeUserId = await gitHelper.getUserIdByLogin(event, dbIssue.assignee);
       if (!assigneeUserId) {
         // The assignement of this user was failed and broken.
         // We don't need to handle the unassignment.
diff --git a/utils/git-helper.js b/utils/git-helper.js
index cea9bea..dd953ac 100644
--- a/utils/git-helper.js
+++ b/utils/git-helper.js
@@ -149,7 +149,7 @@ class GitHelper {
    */
   async getUserIdByLogin(event, assignee) {
     if (event.provider === 'github') {
-      return gitHubService.getUserIdByLogin(event.copilot, assignee);
+      return await gitHubService.getUserIdByLogin(event.copilot, assignee);
     }
     return gitlabService.getUserIdByLogin(event.copilot, assignee);
   }