fix #1124 - return R_NilValue for null pointer objects

This fixes #1124 and returns R_NilValue for null pointer objects

CHANGES.current

@@ -6,6 +6,8 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 
 Version 4.0.0 (in progress)
 ===========================
+2017-11-24: joequant
+	    Fix github #1124 and return R_NilValue for null pointers
 
 2017-10-26: wsfulton
             Add support for C++11 ref-qualifiers when using directors.

Lib/r/rrun.swg

@@ -260,6 +260,9 @@ AddOutputArgToReturn(int pos, SEXP value, const char *name, SEXP output)
 /* Create a new pointer object */
 SWIGRUNTIMEINLINE SEXP
 SWIG_R_NewPointerObj(void *ptr, swig_type_info *type, int flags) {
+  if (!ptr) {
+     return R_NilValue;
+  }
   SEXP rptr = R_MakeExternalPtr(ptr, 
   R_MakeExternalPtr(type, R_NilValue, R_NilValue), R_NilValue); 
   SET_S4_OBJECT(rptr);