core: make allowed track sections non-nullable across core

That way, stdcm and the pathfinding api both take an empty set as input
should we want to have no track section restriction

Signed-off-by: Martin Bourbier <mbourbier28@gmail.com>

Author: MartinBourbier

core/src/main/kotlin/fr/sncf/osrd/api/stdcm/STDCMEndpoint.kt

@@ -598,11 +598,11 @@ private fun parseSimulationScheduleItems(
     )
 }
 
-fun parseTrackSectionIds(infra: FullInfra, trackSectionNames: Set<String>?): Set<TrackSectionId>? {
+fun parseTrackSectionIds(infra: FullInfra, trackSectionNames: Set<String>): Set<TrackSectionId>? {
     return trackSectionNames
-        ?.mapNotNull { infra.rawInfra.getTrackSectionFromName(it) }
-        ?.toSet()
-        ?.takeIf { it.isNotEmpty() }
+        .mapNotNull { infra.rawInfra.getTrackSectionFromName(it) }
+        .toSet()
+        .takeIf { it.isNotEmpty() }
 }
 
 private fun progressCallback(

core/src/main/kotlin/fr/sncf/osrd/api/stdcm/STDCMRequest.kt

@@ -57,7 +57,7 @@ class STDCMRequest(
     @Json(name = "temporary_speed_limits")
     val temporarySpeedLimits: Collection<STDCMTemporarySpeedLimit>,
     @Json(name = "work_schedules") val workSchedules: Collection<WorkSchedule> = listOf(),
-    @Json(name = "allowed_track_sections") val allowedTrackSections: Set<String>?,
+    @Json(name = "allowed_track_sections") val allowedTrackSections: Set<String> = emptySet(),
 )
 
 data class STDCMTemporarySpeedLimit(