diff --git a/platform/script-debugger/protocol/protocol-reader-runtime/src/org/jetbrains/jsonProtocol/OutMessage.kt b/platform/script-debugger/protocol/protocol-reader-runtime/src/org/jetbrains/jsonProtocol/OutMessage.kt
index 4e04af8cb877..63a17b083aa4 100644
--- a/platform/script-debugger/protocol/protocol-reader-runtime/src/org/jetbrains/jsonProtocol/OutMessage.kt
+++ b/platform/script-debugger/protocol/protocol-reader-runtime/src/org/jetbrains/jsonProtocol/OutMessage.kt
@@ -201,7 +201,7 @@ open class OutMessage() {
 
   fun writeNullableString(name: String, value: CharSequence?) {
     beginArguments()
-    writer.name(name).value(value!!.toString())
+    writer.name(name).value(value?.toString() ?: null)
   }
 
   companion object {