diff --git a/server/src/theses-dao.js b/server/src/theses-dao.js
index d7dab69..f420c96 100644
--- a/server/src/theses-dao.js
+++ b/server/src/theses-dao.js
@@ -577,36 +577,38 @@ exports.isAccepted = (proposal_id, student_id) => {
 };
 
 exports.notifyRemovedCosupervisors = async (oldProposal, newProposal) => {
-  const oldCosupervisors = oldProposal.co_supervisors.split(", ");
-  const newCosupervisors = newProposal.co_supervisors.split(", ");
-  const removedCosupervisors = oldCosupervisors.filter((cosupervisor) => {
-    return !newCosupervisors.includes(cosupervisor);
-  });
-  for(let cosupervisorEmail of removedCosupervisors) {
-    const teacher = this.getTeacherByEmail(cosupervisorEmail);
-    // -- Email
-    const mailBody = removedCosupervisorTemplate({
-      name: teacher.surname + " " + teacher.name,
-      proposal: newProposal
+  const oldCosupervisors = oldProposal.co_supervisors?.split(", ");
+  const newCosupervisors = newProposal.co_supervisors?.split(", ");
+  if(oldCosupervisors && newCosupervisors) {
+    const removedCosupervisors = oldCosupervisors.filter((cosupervisor) => {
+      return !newCosupervisors.includes(cosupervisor);
     });
-    try {
-      await nodemailer.sendMail({
-        to: cosupervisorEmail,
-        subject: "You have been removed from a thesis proposal",
-        text: mailBody.text,
-        html: mailBody.html,
+    for(let cosupervisorEmail of removedCosupervisors) {
+      const teacher = this.getTeacherByEmail(cosupervisorEmail);
+      // -- Email
+      const mailBody = removedCosupervisorTemplate({
+        name: teacher.surname + " " + teacher.name,
+        proposal: newProposal
       });
-    } catch (e) {
-      console.log("[mail service]", e);
+      try {
+        await nodemailer.sendMail({
+          to: cosupervisorEmail,
+          subject: "You have been removed from a thesis proposal",
+          text: mailBody.text,
+          html: mailBody.html,
+        });
+      } catch (e) {
+        console.log("[mail service]", e);
+      }
+      // -- Website notification
+      db.prepare(
+        "INSERT INTO NOTIFICATIONS(teacher_id, object, content) VALUES(?,?,?)",
+      ).run(
+        teacher.id,
+        "You have been removed from a thesis proposal",
+        mailBody.text,
+      );
     }
-    // -- Website notification
-    db.prepare(
-      "INSERT INTO NOTIFICATIONS(teacher_id, object, content) VALUES(?,?,?)",
-    ).run(
-      teacher.id,
-      "You have been removed from a thesis proposal",
-      mailBody.text,
-    );
   }
 };
 
diff --git a/server/tests/proposal.test.js b/server/tests/proposal.test.js
index 52d1a07..b0f314d 100644
--- a/server/tests/proposal.test.js
+++ b/server/tests/proposal.test.js
@@ -942,3 +942,48 @@ describe("GET /api/start-requests", () => {
       .expect(200);
   });
 });
+
+describe("PATCH /api/proposals/:id", () => {
+  test("Remove a co supervisor", async () => {
+    isLoggedIn.mockImplementation((req, res, next) => {
+      req.user = {
+        email: "maurizio.morisio@teacher.it",
+      };
+      next();
+    });
+
+    const proposal = {
+      id: 1,
+      title: "test",
+      description: "desc test",
+      supervisor: "s234567",
+      co_supervisors: [
+        "marco.torchiano@teacher.it"
+      ],
+      keywords: ["keyword1", "keyword2"],
+      groups: ["SOFTENG"],
+      types: ["EXPERIMENTAL"],
+      required_knowledge: "required knowledge",
+      notes: "notes",
+      expiration_date: "2021-01-01",
+      level: "MSC",
+      cds: "LM-32 (DM270)",
+      manually_archived: 0,
+      deleted: 0
+    };
+
+    getProposal.mockReturnValue(proposal);
+
+    const newProposal = { ...proposal };
+    newProposal.co_supervisors = [];
+
+    const requests = (
+      await request(app)
+        .put("/api/proposals/1")
+        .set("Content-Type", "application/json")
+        .send(newProposal)
+        .expect(200)
+    );
+    expect(requests.body).toEqual({ message: "Proposal updated successfully" });
+  });
+});