Bugfix notification service, added timestamp for substitutes

src/main/java/io/github/paexception/engelsburg/api/controller/reserved/NotificationSettingsController.java

@@ -118,6 +118,6 @@ public List<String> getTimetableTokens(SubstituteNotificationDTO dto) {
 	@Transactional
 	public void deleteInvalidTokens(List<String> invalidTokens) {
 		//Delete all invalid tokens
-		this.tokenRepository.deleteAllByTokenIn(invalidTokens);
+		if (!invalidTokens.isEmpty()) this.tokenRepository.deleteAllByTokenIn(invalidTokens);
 	}
 }

src/main/java/io/github/paexception/engelsburg/api/controller/reserved/SubstituteController.java

@@ -29,9 +29,12 @@
 @AllArgsConstructor
 public class SubstituteController {
 
+	private static long timestamp = 0;
+
 	private final SubstituteRepository substituteRepository;
 	private final NotificationService notificationService;
 
+
 	/**
 	 * Checks if a string is not blank, empty or null.
 	 *
@@ -75,6 +78,8 @@ private static SubstituteModel createSubstitute(int substituteId, SubstituteDTO
 	 */
 	@Transactional
 	public void updateSubstitutes(List<SubstituteDTO> fetchedDTOs, Date date) {
+		timestamp = System.currentTimeMillis();
+
 		List<SubstituteDTO> current = new ArrayList<>();
 		for (SubstituteModel substitute : this.substituteRepository.findAllByDate(date)) {
 			current.add(substitute.toResponseDTO());
@@ -137,6 +142,6 @@ public Result<GetSubstitutesResponseDTO> getSubstitutes(String classNameFilter,
 		//Map substitutes to response dtos and return them
 		List<SubstituteDTO> dtos = new ArrayList<>();
 		for (SubstituteModel substitute : substitutes) dtos.add(substitute.toResponseDTO());
-		return Result.of(new GetSubstitutesResponseDTO(dtos));
+		return Result.of(new GetSubstitutesResponseDTO(dtos, timestamp));
 	}
 }

src/main/java/io/github/paexception/engelsburg/api/endpoint/dto/response/GetSubstitutesResponseDTO.java

@@ -16,5 +16,6 @@
 public class GetSubstitutesResponseDTO {
 
 	private List<SubstituteDTO> substitutes;
+	private long timestamp;
 
 }

src/test/java/io/github/paexception/engelsburg/api/test/service/scheduled/SubstituteParseTest.java

@@ -4,6 +4,9 @@
 import io.github.paexception.engelsburg.api.service.scheduled.SubstituteUpdateService;
 
 import org.junit.jupiter.api.Test;
+import io.github.paexception.engelsburg.api.endpoint.dto.SubstituteDTO;
+import java.sql.Date;
+import java.util.Objects;
 
 import java.sql.Date;
 import java.util.Objects;
@@ -14,7 +17,7 @@ public class SubstituteParseTest {
     public void testSubstituteParse() {
         new SubstituteUpdateService(null, null, null).updateSubstitutes();
     }
-    
+
     @Test
     public void substituteDTOEqualTest() {
         //Correct 5a - 10e