Fix [fa8de77936]: ttk::checkbutton handle empty variable graceful. Patch from Christian Werner.

1 files changed, 12 insertions, 7 deletions

diff --git a/generic/ttk/ttkButton.c b/generic/ttk/ttkButton.c
index c00754b..2cddb09 100644
--- a/generic/ttk/ttkButton.c
+++ b/generic/ttk/ttkButton.c
@@ -489,12 +489,15 @@ static int
 CheckbuttonConfigure(Tcl_Interp *interp, void *recordPtr, int mask)
 {
     Checkbutton *checkPtr = recordPtr;
-    Ttk_TraceHandle *vt = Ttk_TraceVariable(
-	interp, checkPtr->checkbutton.variableObj,
-	CheckbuttonVariableChanged, checkPtr);
-
-    if (!vt) {
-	return TCL_ERROR;
+    Tcl_Obj *varName = checkPtr->checkbutton.variableObj;
+    Ttk_TraceHandle *vt = NULL;
+        
+    if (varName != NULL && *Tcl_GetString(varName) != '\0') {
+        vt = Ttk_TraceVariable(interp, varName,
+	    CheckbuttonVariableChanged, checkPtr);
+        if (!vt) {
+	    return TCL_ERROR;
+        }
     }
 
     if (BaseConfigure(interp, recordPtr, mask) != TCL_OK){
@@ -502,7 +505,9 @@ CheckbuttonConfigure(Tcl_Interp *interp, void *recordPtr, int mask)
 	return TCL_ERROR;
     }
 
-    Ttk_UntraceVariable(checkPtr->checkbutton.variableTrace);
+    if (checkPtr->checkbutton.variableTrace) {
+        Ttk_UntraceVariable(checkPtr->checkbutton.variableTrace);
+    }
     checkPtr->checkbutton.variableTrace = vt;
 
     return TCL_OK;