Explicitly test for empty string.

In puppet version 4 and later, the empty string is considered true.
This means that conditions written as only 'if $var {' may suddenly
end up taking the opposite code path than originally expected. Add
an explicit test for the empty string to avoid this.

manifests/init.pp

@@ -83,7 +83,7 @@ define tsmclient($serveraddress=undef, $nodename=$fqdn,
 	$tsmclient::config::default_inclexcl,
 	$inclexcl)
 
-    if $serveraddress {
+    if $serveraddress and $serveraddress != '' {
 	$tsm_serveraddress = $serveraddress
     } elsif ($tsmclient::config::tsmservers  and
 	     $name in $tsmclient::config::tsmservers) {