Index: /CKEditor/trunk/_source/plugins/scayt/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/scayt/plugin.js	(revision 5517)
+++ /CKEditor/trunk/_source/plugins/scayt/plugin.js	(revision 5518)
@@ -262,6 +262,7 @@
 				if ( scayt_instance && plugin.isScaytReady( this.editor ) )
 				{
-					this.contents = scayt_instance.reset( thisContents );
-					otherImage.contents = scayt_instance.reset( otherContents );
+					// scayt::reset might return value undefined. (#5742)
+					this.contents = scayt_instance.reset( thisContents ) || '';
+					otherImage.contents = scayt_instance.reset( otherContents ) || '';
 				}