hotfix: convert Region non-null to nullable

Author: chock-cho

domain/src/main/kotlin/com/dobby/model/experiment/ExperimentPostStats.kt

@@ -4,13 +4,13 @@ import com.dobby.enums.areaInfo.Area
 import com.dobby.enums.areaInfo.Region
 
 data class ExperimentPostStats(
-    val regionName: String,
+    val regionName: String?,
     val areaName: String?,
     val count: Long
 )
 {
-    val region: Region
-        get() = Region.valueOf(regionName)
+    val region: Region?
+        get() = regionName?.let { Region.valueOf(it) }
 
     val area: Area?
         get() = areaName?.let { Area.valueOf(it) }

src/main/kotlin/com/dobby/backend/infrastructure/gateway/experiment/ExperimentPostGatewayImpl.kt

@@ -72,7 +72,7 @@ class ExperimentPostGatewayImpl(
         return experimentPostRepository.countExperimentPostGroupedByRegion()
             .map { row ->
                 ExperimentPostStats(
-                    regionName = row[0] as String,
+                    regionName = row[0] as? String,
                     areaName = row[1] as? String,
                     count = (row[2] as Number).toLong()
                 )