D3js mulitline chart mouseOver

I am trying to adapt this D3js mouse use line diagram example for my multi-line diagram.

It seems that d3.mouse(this)[0]

the function mousemove

generates the following error: "Unable to read property 'sourceEvent' from null".

1 Any idea why I am getting nullEventEvent error?

2 Any advice on how to adapt the mouse following example from single line chart to multi-line chart (n)?

Below is a jsfiddle to demonstrate this issue. (And the solution )

var myApp = angular.module('app', []);
myApp.directive("lineChart", function() {
  return {
    restrict: 'E',
    scope: {
      data: '=',
      id: '@'
    },
    link: function (scope, element, attrs) {
      scope.$watch( 'data', function ( data ) {
        d3.select("#"+attrs.id).select("svg").remove();
        if (data) {
          var margin = {top: 20, right: 20, bottom: 30, left: 40},
              width = element[ 0 ].parentElement.offsetWidth - margin.left - margin.right,
              height = element[ 0 ].parentElement.offsetHeight - margin.top - margin.bottom;
          var parseDate = d3.time.format("%d-%b-%y").parse;
          var x = d3.time.scale()
              .range([0, width]);
          var y = d3.scale.linear()
              .range([height, 0]);
          var xAxis = d3.svg.axis()
              .scale(x)
              .orient("bottom")
              .innerTickSize(-height)
              .ticks(4)
              .outerTickSize(0)
              .tickPadding(5)
              .tickFormat(function(d) { return d3.time.format('%d/%m %H:%M')(new Date(d)); });
          var yAxis = d3.svg.axis()
              .scale(y)
              .orient("left")
              .innerTickSize(-width)
              .outerTickSize(0)
              .tickPadding(10);
          var line = d3.svg.line()
              .x(function(d) { return x(d[0]); })
              .y(function(d) { return y(d[1]); });
          var svg = d3.select(element[0]).append("svg")
              .attr("width", '100%')
              .attr("height", '100%')
              .attr('viewBox','0 0 '+ element[ 0 ].parentElement.offsetWidth +' '+ element[ 0 ].parentElement.offsetHeight )
            .append("g")
              .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
          var minX = d3.min(data, function (item) { return d3.min(item.values, function (d) { return d[0]; }) });
          var maxX = d3.max(data, function (item) { return d3.max(item.values, function (d) { return d[0]; }) });
          var minY = d3.min(data, function (item) { return d3.min(item.values, function (d) { return d[1]; }) });
          var maxY = d3.max(data, function (item) { return d3.max(item.values, function (d) { return d[1]; }) });
          x.domain([minX, maxX]);
          y.domain([0, maxY]);
          svg.append("g")
              .attr("class", "x axis")
              .attr("transform", "translate(0," + height + ")")
              .call(xAxis);
          svg.append("g")
              .attr("class", "y axis")
              .call(yAxis);
          var domaine = svg.selectAll(".domaine")
              .data(data)
              .enter().append("g")
              .attr("class", "domaine");
          domaine.append("path")
              .attr("class", "line")
              .attr("d", function (d) {
                  return line(d.values);
              })
              .style("stroke", function (d) {
                return d.color;
              });
          var focus = svg.append("g")
              .attr("class", "focus")
              .style("display", "none");
          focus.append("circle")
              .attr("r", 4.5);
          focus.append("text")
              .attr("x", 9)
              .attr("dy", ".35em");
          svg.append("rect")
              .attr("class", "overlay")
              .attr("width", width)
              .attr("height", height)
              .on("mouseover", function() { focus.style("display", null); })
              .on("mouseout", function() { focus.style("display", "none"); })
              .on("mousemove", mousemove());
          function mousemove() {              
            var x0 = x.invert(d3.mouse(this)[0]),
                i = bisectDate(data, x0, 1),
                d0 = data[i - 1],
                d1 = data[i];/*
                To adapt for multi line
                ,
                d = x0 - d0.date > d1.date - x0 ? d1 : d0;
            focus.attr("transform", "translate(" + x(d.date) + "," + y(d.close) + ")");
            focus.select("text").text(formatCurrency(d.close));*/
          }
        }
      });
    }
  };
});
function MainCtrl($scope) {
$scope.lineData = [{"key": "users","color": "#16a085",
"values": [[1413814800000,4034.418],[1413815400000,5604.155000000001]]},
{"key": "users 2","color": "#d95600",
"values": [[1413814800000,3168.183],[1413815400000,1530.8435]]}];
}