diff --git a/modules/swagger-codegen/src/main/resources/swift/APIHelper.mustache b/modules/swagger-codegen/src/main/resources/swift/APIHelper.mustache
index e562ae92cf4f..7041709f3651 100644
--- a/modules/swagger-codegen/src/main/resources/swift/APIHelper.mustache
+++ b/modules/swagger-codegen/src/main/resources/swift/APIHelper.mustache
@@ -19,16 +19,18 @@ class APIHelper {
         return destination
     }
 
-    static func convertBoolToString(source: [String: AnyObject]) -> [String:AnyObject] {
+    static func convertBoolToString(source: [String: AnyObject]?) -> [String:AnyObject] {
         var destination = [String:AnyObject]()
         let theTrue = NSNumber(bool: true)
         let theFalse = NSNumber(bool: false)
-        for (key, value) in source {
-            switch value {
-                case let x where x === theTrue || x === theFalse:
-                    destination[key] = "\(value as! Bool)"
-                default:
-                    destination[key] = value
+        if (source != nil) {
+            for (key, value) in source! {
+                switch value {
+                    case let x where x === theTrue || x === theFalse:
+                        destination[key] = "\(value as! Bool)"
+                    default:
+                        destination[key] = value
+                }
             }
         }
         return destination