--- a/UnixOperatingSystem.st	Fri Sep 17 15:46:08 1999 +0200
+++ b/UnixOperatingSystem.st	Fri Sep 17 16:07:58 1999 +0200
@@ -3079,6 +3079,8 @@
 
     |in out err shellAndArgs rslt|
 
+    aCommandString isNil ifTrue:[^ nil].
+
     (in := anExternalInStream) isNil ifTrue:[
         in := '/dev/null' asFilename readStream
     ].
@@ -3094,6 +3096,7 @@
     ].
 
     shellAndArgs := self commandAndArgsForOSCommand:aCommandString.
+
     rslt := self
         exec:(shellAndArgs at:1)
         withArguments:(shellAndArgs at:2)
@@ -8650,6 +8653,6 @@
 !UnixOperatingSystem class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/UnixOperatingSystem.st,v 1.68 1999-07-23 07:34:53 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/UnixOperatingSystem.st,v 1.69 1999-09-17 14:07:58 cg Exp $'
 ! !
 UnixOperatingSystem initialize!