fix: calculate nextRunAt when endDate is undefined (#1227)

for backward compatibility check that endDate and startDate are defined when calculating nextRunAt value.
when upgrading from an older version of agenda those fields could be missing from the job and fail the computation of nextRunAt
with 'failed to calculate nextRunAt due to an invalid repeat interval' exception
this solves agenda/agenda#1224

Author: talik077

lib/job/compute-next-run-at.ts

@@ -62,7 +62,7 @@ export const computeNextRunAt = function (this: Job) {
       }
 
       // If start date is present, check if the nextDate should be larger or equal to startDate. If not set startDate as nextDate
-      if (startDate !== null) {
+      if (startDate) {
         startDate = moment
           .tz(moment(startDate).format("YYYY-MM-DD"), timezone!)
           .toDate();
@@ -83,7 +83,7 @@ export const computeNextRunAt = function (this: Job) {
       }
 
       // If endDate is less than the nextDate, set nextDate to null to stop the job from running further
-      if (endDate !== null) {
+      if (endDate) {
         const endDateDate: Date = moment
           .tz(moment(endDate).format("YYYY-MM-DD"), timezone!)
           .toDate();

test/job.js

@@ -355,6 +355,15 @@ describe("Job", () => {
         job.computeNextRunAt();
         expect(job.attrs.nextRunAt).to.be(undefined);
       });
+
+      it("sets the correct interval when endDate is undefined", () => {
+        // (Issue #1224): failed to calculate nextRunAt when endDate is undefined
+        job.repeatEvery("0 0 * * *"); // Daily at midnight
+        job.attrs.endDate = undefined;
+        job.computeNextRunAt();
+        expect(job.attrs.failCount).to.be(undefined);
+        expect(job.attrs.nextRunAt).not.to.be(undefined);
+      });
     });
 
     it("gives the correct nextDate when the lastRun is 1ms before the expected time", () => {