diff --git a/core/src/main/kotlin/timetables/service/TimetableThemeService.kt b/core/src/main/kotlin/timetables/service/TimetableThemeService.kt
index b224ccfa..9b43eef3 100644
--- a/core/src/main/kotlin/timetables/service/TimetableThemeService.kt
+++ b/core/src/main/kotlin/timetables/service/TimetableThemeService.kt
@@ -238,7 +238,8 @@ class TimetableThemeServiceImpl(
             val theme = getTheme(timetable.userId, timetable.themeId)
 
             val alreadyUsedColors = timetable.lectures.map { requireNotNull(it.color) }
-            val colorToCount = requireNotNull(theme.colors).associateWith { color -> alreadyUsedColors.count { it == color } }
+            val colors = requireNotNull(theme.colors) { "theme.colors 가 null - userId: ${timetable.userId}, timetableId: ${timetable.id}, themeId: ${theme.id}" }
+            val colorToCount = colors.associateWith { color -> alreadyUsedColors.count { it == color } }
 
             val minCount = colorToCount.minOf { it.value }
             0 to colorToCount.entries.filter { (_, count) -> count == minCount }.map { it.key }.random()