Resolve "[Queue-2.0] Repeat lab does not work for selection labs"

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Closes #520 (closed)

src/main/java/nl/tudelft/queue/dto/create/labs/CapacitySessionCreateDTO.java

@@ -77,7 +77,10 @@ public class CapacitySessionCreateDTO extends QueueSessionCreateDTO<CapacitySess
 				.setEnrolmentOpensAt(capacitySessionConfig.getEnrolmentOpensAt().plusWeeks(weeks));
 		capacitySessionConfig
 				.setEnrolmentClosesAt(capacitySessionConfig.getEnrolmentClosesAt().plusWeeks(weeks));
-		capacitySessionConfig.setSelectionAt(capacitySessionConfig.getSelectionAt().plusWeeks(weeks));
+		capacitySessionConfig
+				.setSelectionAt((capacitySessionConfig.getSelectionAt() != null)
+						? capacitySessionConfig.getSelectionAt().plusWeeks(weeks)
+						: null);
 	}
 
 	@Override