asp.net-mvc – Web api删除方法输入对象参数为null

那么是什么导致webapi asp.net方法中的联系对象参数作为空值进入？

我已经如图所示检查了角度控制器内的接触对象在传递给webapi delete方法之前不是null.

Here is my rest of the code 

  <div data-ng-controller="ContactDeleteController">
        <form name ="deleteContact" data-ng-submit="saveDeleteContact()">
            <div>
                <label>First Name: </label>
                <input required type="text" placeholder="Enter First Name" data-ng-model="contact.FirstName"/>
            </div>
            <div>
                <label>Last Name: </label>
                <input required type="text" placeholder="Enter Last Name" data-ng-model="contact.LastName"/>
            </div>
            <div>
                <label>Email Address: </label>
                <input required type="text" placeholder="Enter Email Address" data-ng-model="contact.EmailAddress"/>
            </div>
            <div>
                <label>Cell Phone Number: </label>
                <input required type="text" placeholder="Enter Phone Number" data-ng-model="contact.PhoneNumber"/>
            </div>
            <div></div>
            <div>
                <button class="btn btn-primary" type="submit">Delete</button>
            </div>
        </form>
    </div>



    var ContactDeleteController = function ($scope,$http,$location) {
        var contactId = $location.absUrl().match(//Delete/(.*)/)[1];
        $http.get("/api/ContactWeb/" + contactId)
            .then(function (response) {
                $scope.contact = response.data;
            });

        $scope.saveDeleteContact = function () {
            var con = $scope.contact;
            $http.delete("/api/ContactWeb",con)
                .then(function (response) {
                    $scope.contact = response.data;
                });
            window.location = "/Contact/Index";
        };
    };