o The NSE nmap.registry.args table is now available, albeit empty, when

--script-args isn't used.  Now scripts don't need to check if it's nil
  before attempting to index it. [Kris]

CHANGELOG

@@ -180,6 +180,10 @@ o Fix a couple bugs in the way the Nmap built system checked for an
   configure option for specifying your own liblua. [Daniel
   Roethlisberger]
 
+o The NSE nmap.registry.args table is now available, albeit empty, when
+  --script-args isn't used.  Now scripts don't need to check if it's nil
+  before attempting to index it. [Kris]
+
 o Changed SSLv2-support.nse so that it only enumerates the list of
   available ciphers with a verbosity level of at least two or with
   debugging enabled. [Kris]

NmapOps.cc

@@ -456,7 +456,10 @@ void NmapOps::ValidateOptions() {
 
   if(ipoptions && osscan)
     error("WARNING: Ip options are NOT used while OS scanning!");
-    
+
+  /* Make sure nmap.registry.args is available (even if it's empty) */
+  if (!scriptargs)
+    scriptargs = strdup("");
 }
 
 void NmapOps::setMaxOSTries(int mot) {

nse_init.cc

@@ -285,7 +285,7 @@ int init_lua (lua_State *L)
 /* int init_parseargs (lua_State *L)
  *
  * Arguments
- *   args    Arguments passed through --script-args
+ *   args    Arguments passed through --script-args, or "" if it wasn't used
  * Returns
  *   function    Function that returns a table with the arguments, or an error
  *               message describing why the arguments could not be parsed.
@@ -320,9 +320,6 @@ int init_parseargs (lua_State *L)
  */
 int init_setargs (lua_State *L)
 {
-  if (o.scriptargs == NULL)
-    return 0;
-
   lua_getglobal(L, "nmap");
   lua_getfield(L, -1, "registry");