string as the parameter:
now you would expect to see something like "received
test-value: (type String)" on your screen.
but instead you will see something like "received test-value:
null (type String)".
somehow, in ExternalInterface, the empty string parameter is
transformed into a "null" value, which in turn is transformed back
into a string-value containing the text "null".
My workaround so far is not pretty - I detect empty strings
"__EMPTY_STRING__", and then detect this string in my movie, and
replace it back with an actual empty string.
ExternalInterface injects into Internet Explorer - most likely, it
does a .toString() on a null-value or something, as it's composing
the XML command string for the Flash player.