Bugfix WriteLineAsync(String value) to not crash on writing null string

diff --git a/mcs/class/referencesource/mscorlib/system/io/streamwriter.cs b/mcs/class/referencesource/mscorlib/system/io/streamwriter.cs
index 784d468a5b9709cc155d95febb19fb00c21b0558..98d76c9936288862138167f1a1f711d426fed817 100644 (file)
--- a/mcs/class/referencesource/mscorlib/system/io/streamwriter.cs
+++ b/mcs/class/referencesource/mscorlib/system/io/streamwriter.cs
@@ -756,7 +756,7 @@ namespace System.IO
 
             CheckAsyncTaskInProgress();
 
-            Task task = WriteAsyncInternal(this, value, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: true);
+            Task task = WriteAsyncInternal(this, value ?? "", charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: true);
             _asyncWriteTask = task;
 
             return task;