This code is a part of my project that I am trying to make force-layout graph in it. All links between nodes should have a marker that I make them (the markers) by the means of defs patterns.  

In this code I expect to see defined markers in `defs` where I have called them by `url(#id)` but I do not see it while I get no error. It was working before but suddenly all `defs` has been disabled in my code.
Here you see the result svg: 

```html
<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  font: 10px sans-serif;
  shape-rendering: crispEdges;
}

.link.flow {
    opacity: 1!important;
    /*stroke-width: 1.5px;*/
}

#licensing {
    fill: green;
}

.link.flow.licensing {
    stroke: green;
}

.link.flow.resolved {
    stroke-dasharray: 0,2 1;
}

circle.flow {
    fill: #ff2575;
    stroke: #ff2575;
    /*stroke-width: 1.5px;*/
}

text.flow {
    font: 10px sans-serif;
    pointer-events: none;
    text-shadow: 0 1px 0 #fff, 1px 0 0 #fff, 0 -1px 0 #fff, -1px 0 0 #fff;
}

path.link.flow {
    fill: none;
 stroke: blue;
}

</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
<script>
var maxWeight = 0;
var maxSize = 0;

//  new graph: start
var margin = 10;
var width = 455,
 height = 350;

var svgMaster = d3.select("body").append("svg") //  initiate svg
 .attr("id","flow")
 .attr("width", width)
 .attr("height", height)
 .style("margin-right",margin+"px")
 .style("margin-left",margin+"px");

var svg = svgMaster.append('svg:g')
 .attr('id','groupFlow');

var link = svg.selectAll(".link"),
 node = svg.selectAll(".node");  //  nodes and links
// :end new graph

var jsonData = {
 "nodes": [
  {"username": "S_Christophorus", "social_net_id": "55641120cdfa6618acdd1952", "last_name":
   "Christophorus", "first_name": "Stanly", "avatar": "/media/avatars/C02.png", "person_id": "556431f3cdfa661108325774"
  , "id": "55641120cdfa6618acdd1a8e"},
  {"username": "A_Field", "social_net_id": "55641120cdfa6618acdd1952"
  , "last_name": "Field", "first_name": "Abdul", "avatar": "/media/avatars/B01.png", "person_id": "556431f3cdfa6611083257f6"
  , "id": "55641120cdfa6618acdd1b94"}, 
  {"username": "B_Hugh", "social_net_id": "55641120cdfa6618acdd1952"
  , "last_name": "Hugh", "first_name": "Beale", "avatar": "/media/avatars/B02.png", "person_id": "556431f3cdfa6611083257f7"
  , "id": "55641120cdfa6618acdd1b96"}, 
  {"username": "M_Kennedy", "social_net_id": "55641120cdfa6618acdd1952"
  , "last_name": "Kennedy", "first_name": "Mordy", "avatar": "/media/avatars/B05.png", "person_id": "556431facdfa661108327e21"
  , "id": "55641128cdfa6618acdd9fed"}
 ], 
 "edges": [
  {"source": 0, "target": 1, "weight": 1.5}, 
  {"source": 2, "target": 0, "weight": 46.5}, 
  {"source": 0, "target": 2, "weight": 6.0}, 
  {"source": 2, "target": 1, "weight": 1.5}, 
  {"source": 2, "target": 3, "weight": 3.0}
 ]
}

/*
 * refresh graph based on given data
 */
var refreshForceFlow = function(json){
 clearGraphFlow();
 var maxWeight = 0;

    for(var edgeIndex = 0; edgeIndex < json.edges.length; edgeIndex++){
      if(json.edges[edgeIndex].weight > maxWeight) maxWeight = json.edges[edgeIndex];
      }
   console.log(json);
 var force = d3.layout.force()
  .nodes(d3.values(json.nodes))
  .links(json.edges)
  .size([width, height])
  .linkDistance(60)
  .charge(-300)
  .on("tick", tickFlow)
  .start();

 // Per-type markers, as they don't inherit styles.
 svg.append("defs").selectAll("marker")
  .data(json.edges)
  .enter().append("marker")
  .attr("id", function(d) { return ("weight_"+d.weight).replace(".","_"); })
  .attr("viewBox", "0 -5 10 10")
  .attr("refX", 13)    //  15
  .attr("refY", 0)    //  -1.5
  .attr("markerWidth", 6)
  .attr("markerHeight", 6)
  .attr("orient", "auto")
  .append("path")
  .style("fill", function(d){
   var color = 'FF';
   var c = Math.floor((d.weight*99)/maxWeight);
   c = 100 - c;
   if( c < 10) c = '0'+c;
   color = c + color;
   color = c + color;
   //console.log('#'+color);
   return '#'+color;
  })
  .style("stroke", function(d){
   var color = 'FF';
   var c = Math.floor((d.weight*99)/maxWeight);
   c = 100 - c;
   if( c < 10) c = '0'+c;
   color = c + color;
   color = c + color;
   //console.log('#'+color);
   return '#'+color;
  })
  .style("stroke-width", "1px")
  .attr("d", "M0,-5L10,0L0,5");

 var path = svg.append("g").selectAll("path")
  .data(force.links())
  .enter().append("path")
  .attr("class", function(d) { return "link flow "; })
  .style("stroke-width", function(d) {
   var res = 1 + ((d.weight * 2.5) / maxWeight);
   return res + 'px';
  })
  .style("stroke", function(d){
   var color = 'FF';
   var c = Math.floor((d.weight*99)/maxWeight);
   c = 100 - c;
   if( c < 10) c = '0'+c;
   color = c + color;
   color = c + color;
   //console.log('#'+color);
   return '#'+color;
  })
  .attr("marker-end", function(d) { return "url(#" + ("weight_"+d.weight).replace(".","_") + ")"; });

 var circle = svg.append("g").selectAll("circle")
  .data(force.nodes())
  .enter().append("circle")
  .attr("r", 6)
  .attr("class", "flow")
  .call(force.drag);

 var text = svg.append("g").selectAll("text")
  .data(force.nodes())
  .enter().append("text")
  .attr("class", "flow")
  .attr("x", 8)
  .attr("y", ".31em")
  .text(function(d) { return d.username; });

 // Use elliptical arc path segments to doubly-encode directionality.
 function tickFlow() {
  path.attr("d", linkArc);
  circle.attr("transform", transform);
  text.attr("transform", transform);
 }

 function linkArc(d) {
  var tx = d.target.x - 0;
  var ty = d.target.y - 0;
  var sx = d.source.x - 0;
  var sy = d.source.y - 0;

  var dx = tx - sx,
   dy = ty - sy,
   dr = Math.sqrt(dx * dx + dy * dy);
  return "M" + d.source.x + "," + d.source.y + "A" + dr + "," + dr + " 0 0,1 " + d.target.x + "," + d.target.y;
 }

 function transform(d) {
  return "translate(" + d.x + "," + d.y + ")";
 }
};  //  end of function

/*
 * clear gragh
 */
var clearGraphFlow = function(){
 svg.selectAll("g").remove();
 svg.selectAll("defs").remove();
};

refreshForceFlow(jsonData);

</script>
```