[gegl] Provide a non-null input pad for unconnected nodes

[Daniel Sabo <daniels src gnome org>]

commit 9133f8ced09260c83b0332b49f5dca3bfef08ecf
Author: Daniel Sabo <DanielSabo gmail com>
Date:   Tue May 21 23:08:30 2013 -0700

    Provide a non-null input pad for unconnected nodes

 gegl/process/gegl-eval-visitor.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)
---
diff --git a/gegl/process/gegl-eval-visitor.c b/gegl/process/gegl-eval-visitor.c
index 6eac5f7..aa62838 100644
--- a/gegl/process/gegl-eval-visitor.c
+++ b/gegl/process/gegl-eval-visitor.c
@@ -154,7 +154,8 @@ gegl_eval_visitor_visit_pad (GeglVisitor *self,
     }
   else if (gegl_pad_is_input (pad))
     {
-      GeglPad *source_pad = gegl_pad_get_connected_to (pad);
+      GeglPad     *source_pad = gegl_pad_get_connected_to (pad);
+      const gchar *pad_name   = gegl_pad_get_name (pad);
 
       /* the work needed to be done on input pads is to set the
        * data from the corresponding output pad it is connected to
@@ -180,8 +181,8 @@ gegl_eval_visitor_visit_pad (GeglVisitor *self,
                        g_value_get_object (&value));
 
           gegl_operation_context_set_property (context,
-                                          gegl_pad_get_name (pad),
-                                          &value);
+                                               pad_name,
+                                               &value);
           /* reference counting for this source dropped to zero, freeing up */
           if (-- gegl_node_get_context (
                      gegl_pad_get_node (source_pad), context_id)->refs == 0 &&
@@ -208,5 +209,12 @@ gegl_eval_visitor_visit_pad (GeglVisitor *self,
                 &context->result_rect, context->level);
             }
         }
+      else if (!strcmp (pad_name, "input"))
+        {
+          /* Guarantee a non-null input pad for unconnected nodes */
+          gegl_operation_context_take_object (context,
+                                              pad_name,
+                                              gegl_eval_visitor_get_shared_empty (self));
+        }
     }
 }