Fix programme page

src/main/java/nl/tudelft/portal/controller/ProgramController.java

@@ -17,6 +17,7 @@
  */
 package nl.tudelft.portal.controller;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
 
@@ -74,7 +75,8 @@ public class ProgramController {
 	public String getProgrammes(@AuthenticatedPerson Person person, Model model) {
 		List<Long> programIds = programApi.getAllRelevantPrograms(person.getId()).collectList()
 				.block().stream().map(ProgramSummaryDTO::getId).collect(Collectors.toList());
-		List<ProgramDetailsDTO> programs = programApi.getAllProgramsById(programIds).collectList().block();
+		List<ProgramDetailsDTO> programs = programIds.isEmpty() ? Collections.emptyList()
+				: programApi.getAllProgramsById(programIds).collectList().block();
 		model.addAttribute("programs", programs);
 		model.addAttribute("program", new PortalProgramCreateDTO());
 		model.addAttribute("patch", new PortalProgramPatchDTO());
@@ -94,12 +96,16 @@ public class ProgramController {
 	@PreAuthorize("@authorisationService.canManageProgram(#id)")
 	public String getProgram(@AuthenticatedPerson Person person, @PathVariable Long id, Model model) {
 		ProgramDetailsDTO program = programApi.getProgramById(id).block();
-		List<CourseDetailsDTO> courses = courseApi.getAllCoursesById(
-				program.getCourses().stream().map(CourseSummaryDTO::getId).collect(Collectors.toList()))
-				.collectList().block();
-		List<CohortDetailsDTO> cohorts = cohortApi.getAllCohortsById(
-				program.getCohorts().stream().map(CohortSummaryDTO::getId).collect(Collectors.toList()))
-				.collectList().block();
+		List<CourseDetailsDTO> courses = program.getCourses().isEmpty() ? Collections.emptyList()
+				: courseApi.getAllCoursesById(
+						program.getCourses().stream().map(CourseSummaryDTO::getId)
+								.collect(Collectors.toList()))
+						.collectList().block();
+		List<CohortDetailsDTO> cohorts = program.getCohorts().isEmpty() ? Collections.emptyList()
+				: cohortApi.getAllCohortsById(
+						program.getCohorts().stream().map(CohortSummaryDTO::getId)
+								.collect(Collectors.toList()))
+						.collectList().block();
 
 		model.addAttribute("program", program);
 		model.addAttribute("courses", courses);