add some more safety checks for NULL parameters.

diff --git a/tclpkg/gv/gv.cpp b/tclpkg/gv/gv.cpp
index 3e6f3bb6ac1e141e31ff76d2cf9e8f434bdfc09e..029c9b09ac44272c6bd2b940e51cbd4593b041e1 100644 (file)
--- a/tclpkg/gv/gv.cpp
+++ b/tclpkg/gv/gv.cpp
@@ -611,11 +611,15 @@ Agedge_t *nextout(Agraph_t *g, Agedge_t *e)
 
 Agedge_t *firstedge(Agraph_t *g)
 {
+    if (!g)
+       return NULL;
     return firstout(g);
 } 
 
 Agedge_t *nextedge(Agraph_t *g, Agedge_t *e)
 {
+    if (!g || !e)
+       return NULL;
     return nextout(g, e);
 } 
 
@@ -748,11 +752,15 @@ Agnode_t *nexttail(Agnode_t *n, Agnode_t *t)
 
 Agnode_t *firstnode(Agraph_t *g)
 {
+    if (!g)
+       return NULL;
     return agfstnode(g);
 }
 
 Agnode_t *nextnode(Agraph_t *g, Agnode_t *n)
 {
+    if (!g || !n)
+       return NULL;
     return agnxtnode(g, n);
 }