Angular Number Picker Directive Expression is undefined - angularjs

Question

I've read a few questions having to do with this topic and cannot figure out what I'm missing in my own direcitve.
angular.module('app')
.directive('numberPicker', [NumberPicker]);
function NumberPicker () {
var getTarget, getType;
getTarget = function (e) { return angular.element(e.target); }
getType = function (e) { return getTarget(e).attr('direction-type'); }
return {
restrict: 'E',
replace: true,
require: 'ngModel',
scope: {
value: '='
},
template: '<div class="ui action input">' +
'<input value="{{value}}" type="text" />' +
'<button class="ui icon button" type="button" direction-type="up" ng-class="{disabled : canUp === false}">' +
'<i class="angle up icon" direction-type="up"></i>' +
'</button>' +
'<button class="ui icon button" type="button" direction-type="down" ng-class="{disabled : canDown === false}">' +
'<i class="angle down icon" direction-type="down"></i>' +
'</button>' +
'</div>',
controller: function ($scope) {},
link: function (scope, element, attrs, ctrl) {
scope.value = 0;
var options = {
min: 0,
max: 10,
step: 1
};
scope.$watch('value', function (newValue) {
scope.canDown = newValue > options.min;
scope.canUp = newValue < options.max;
if (ctrl.$viewValue != newValue) {
ctrl.$setViewValue(newValue);
}
});
var changeNumber = function (event) {
var type = getType(event);
if ('up' === type) {
if (scope.value >= options.max) {
return;
}
scope.value += options.step;
}
if ('down' === type) {
if (scope.value <= options.min) {
return;
}
scope.value -= options.step;
}
}
var btn = element.find('button');
var input = element.find('input');
btn.on('click', function (e) {
scope.$apply(function () {
changeNumber(e);
});
e.preventDefault();
});
input.on('change', function (e) {
scope.value = input[0].value;
scope.$apply();
})
scope.$on('$destroy', function () {
btn.off('touchstart touchend click')
});
}
}
}
The purpose of this was to create a number picker form element for Semantic UI. It was working perfectly a few days ago. And this error is so vague I can't even process where to start. Did I mention I am an Angular noob?
The error is :
Error: [$compile:nonassign] Expression 'undefined' used with directive 'numberPicker' is non-assignable!

Answer 1

How do you use the directive?
According to the definition you need to have both attributes "value" and "ng-model" set.
For example:
<number-picker value="xyz" ng-model="abc"></number-picker>
The error "Expression 'undefined' used with directive..." is normally thrown if one of the scope values is not set.