Update backend to handle when stage start date and stage end date is null

src/main/java/com/ffii/tsms/modules/project/service/ProjectsService.kt

@@ -286,8 +286,8 @@ open class ProjectsService(
                 val requestMilestone = request.milestones[taskStageId]
                 this.project = project
                 this.taskGroup = taskGroupMap[taskStageId]
-                this.startDate = requestMilestone?.startDate?.let { LocalDate.parse(it) }
-                this.endDate = requestMilestone?.endDate?.let { LocalDate.parse(it) }
+                this.startDate = requestMilestone?.startDate?.let { LocalDate.parse(it) } ?: request.projectPlanStart
+                this.endDate = requestMilestone?.endDate?.let { LocalDate.parse(it) } ?: request.projectPlanEnd
                 if (this.milestonePayments.isNotEmpty()) {
                     this.milestonePayments.removeAll(this.milestonePayments)
                 }