Fix selection at may not be null for FCFS

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src/main/java/nl/tudelft/queue/dto/create/embeddables/CapacitySessionConfigCreateDTO.java

@@ -59,7 +59,6 @@ public class CapacitySessionConfigCreateDTO extends Create<CapacitySessionConfig
 	/**
 	 * The time at which to execute picking and show students who got picked.
 	 */
-	@NotNull
 	@DateTimeFormat(pattern = TIME_FORMAT)
 	private LocalDateTime selectionAt;
 
@@ -70,6 +69,15 @@ public class CapacitySessionConfigCreateDTO extends Create<CapacitySessionConfig
 		this.selectionAt = config.getSelectionAt();
 	}
 
+	@Override
+	protected void postApply(CapacitySessionConfig data) {
+		super.postApply(data);
+
+		if (selectionAt == null && procedure.isFcfs()) {
+			data.setSelectionAt(enrolmentClosesAt);
+		}
+	}
+
 	@Override
 	public Class<CapacitySessionConfig> clazz() {
 		return CapacitySessionConfig.class;