add: if (this.c == null) return false; 
context:     this.showHeaders = function()    {        for (i=0;i<this.matrix[this.r].cells[this.c].headers.length;i++) {            document.getElementById("td" + this.matrix[this.r].cells[this.c].headers[i].r + "_" + this.matrix[this.r].cells[this.c].headers[i].c).style.background = "url(" + this.semired + ")";        }    }
meta: 5635	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/5635/a56d7cfe6ba3204593086a43fcd2394ac00d787a/table-editor.js/buggy/fudge/wysiwyg/plugins/table_editing/table-editor.js