fix: remove precondition() from BTKClient

Bucketeer/Sources/Public/BKTClient.swift

@@ -73,8 +73,10 @@ public class BKTClient {
 }
 
 extension BKTClient {
-    public static func initialize(config: BKTConfig, user: BKTUser, timeoutMillis: Int64 = 5000, completion: ((BKTError?) -> Void)? = nil) {
-        precondition(Thread.isMainThread, "the initialize method must be called on main thread")
+    public static func initialize(config: BKTConfig, user: BKTUser, timeoutMillis: Int64 = 5000, completion: ((BKTError?) -> Void)? = nil) throws {
+        guard (Thread.isMainThread) else {
+            throw BKTError.illegalState(message: "the initialize method must be called on main thread")
+        }
         concurrentQueue.sync {
             guard BKTClient.default == nil else {
                 config.logger?.warn(message: "BKTClient is already initialized. Not sure if the initial fetch has finished")
@@ -98,22 +100,23 @@ extension BKTClient {
         }
     }
 
-    public static func destroy() {
-        precondition(Thread.isMainThread, "the destroy method must be called on main thread")
+    public static func destroy() throws {
+        guard (Thread.isMainThread) else {
+            throw BKTError.illegalState(message: "the destroy method must be called on main thread")
+        }
         BKTClient.default?.resetTasks()
         BKTClient.default = nil
     }
 
     public static var shared: BKTClient {
         get throws {
+            // We do not want to crash the SDK's consumer app on runtime by using fatalError().
+            // So let the app has a chance to catch this exception
+            // The same behavior with the Android SDK
             guard BKTClient.default != nil else {
                 throw BKTError.illegalState(message: "BKTClient is not initialized")
             }
             return BKTClient.default
-            // We do not want to crash the SDK's consumer app on runtime by using fatalError().
-            // So let the app has a chance to catch this exception
-            // The same behavior with the Android SDK
-
         }
     }