diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..fa29cdf
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1 @@
+**
\ No newline at end of file
diff --git a/build/js/tempusdominus-core.js b/build/js/tempusdominus-core.js
index 6337cf9..f1f6e55 100644
--- a/build/js/tempusdominus-core.js
+++ b/build/js/tempusdominus-core.js
@@ -5,7 +5,10 @@ function _classCallCheck(instance, Constructor) { if (!(instance instanceof Cons
 // ReSharper disable once InconsistentNaming
 var DateTimePicker = function ($, moment) {
     // ReSharper disable InconsistentNaming
-    var NAME = 'datetimepicker',
+    var trim = function trim(str) {
+        return str.replace(/(^\s+)|(\s+$)/g, '');
+    },
+        NAME = 'datetimepicker',
         DATA_KEY = '' + NAME,
         EVENT_KEY = '.' + DATA_KEY,
         DATA_API_KEY = '.data-api',
@@ -288,7 +291,7 @@ var DateTimePicker = function ($, moment) {
         enabledHours: false,
         viewDate: false,
         allowMultidate: false,
-        multidateSeparator: ','
+        multidateSeparator: ', '
     };
 
     // ReSharper restore InconsistentNaming
@@ -418,6 +421,7 @@ var DateTimePicker = function ($, moment) {
                 } else {
                     outpValue = this._dates[index].format(this.actualFormat);
                 }
+                outpValue = trim(outpValue);
                 if (this.input !== undefined) {
                     this.input.val(outpValue);
                     this.input.trigger('input');
@@ -526,7 +530,7 @@ var DateTimePicker = function ($, moment) {
         };
 
         DateTimePicker.prototype._notifyEvent = function _notifyEvent(e) {
-            if (e.type === DateTimePicker.Event.CHANGE && (e.date && e.date.isSame(e.oldDate)) || !e.date && !e.oldDate) {
+            if (e.type === DateTimePicker.Event.CHANGE && e.date && e.date.isSame(e.oldDate) || !e.date && !e.oldDate) {
                 return;
             }
             this._element.trigger(e);
@@ -570,7 +574,7 @@ var DateTimePicker = function ($, moment) {
         };
 
         DateTimePicker.prototype._isValid = function _isValid(targetMoment, granularity) {
-            if (!targetMoment.isValid()) {
+            if (!targetMoment || !targetMoment.isValid()) {
                 return false;
             }
             if (this._options.disabledDates && granularity === 'd' && this._isInDisabledDates(targetMoment)) {
@@ -1458,8 +1462,8 @@ var DateTimePicker = function ($, moment) {
                 return this._options.multidateSeparator;
             }
 
-            if (typeof _multidateSeparator !== 'string' || _multidateSeparator.length > 1) {
-                throw new TypeError('multidateSeparator expects a single character string parameter');
+            if (typeof _multidateSeparator !== 'string') {
+                throw new TypeError('multidateSeparator expects a string parameter');
             }
 
             this._options.multidateSeparator = _multidateSeparator;
diff --git a/package.json b/package.json
index 4244977..f0f118f 100644
--- a/package.json
+++ b/package.json
@@ -9,6 +9,9 @@
   "bugs": {
     "url": "https://github.com/tempusdominus/core/issues"
   },
+  "scripts": {
+    "build": "grunt"
+  },
   "dependencies": {
     "jquery": "^3.0",
     "moment": "^2.22.2",
@@ -55,4 +58,4 @@
     "src/js/**/*.js",
     "Gruntfile.js"
   ]
-}
+}
\ No newline at end of file
diff --git a/src/js/tempusdominus-core.js b/src/js/tempusdominus-core.js
index 8c4b5b3..d149d74 100644
--- a/src/js/tempusdominus-core.js
+++ b/src/js/tempusdominus-core.js
@@ -3,8 +3,13 @@ import moment from 'moment';
 
 // ReSharper disable once InconsistentNaming
 const DateTimePicker = (($, moment) => {
+    function escapeRegExp(text) {
+        return text.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, '\\$&');
+    }
+
     // ReSharper disable InconsistentNaming
-    const NAME = 'datetimepicker',
+    const trim = str => str.replace(/(^\s+)|(\s+$)/g, ''),
+        NAME = 'datetimepicker',
         DATA_KEY = `${NAME}`,
         EVENT_KEY = `.${DATA_KEY}`,
         DATA_API_KEY = '.data-api',
@@ -287,7 +292,7 @@ const DateTimePicker = (($, moment) => {
         enabledHours: false,
         viewDate: false,
         allowMultidate: false,
-        multidateSeparator: ','
+        multidateSeparator: ', '
     };
 
     // ReSharper restore InconsistentNaming
@@ -424,11 +429,16 @@ const DateTimePicker = (($, moment) => {
                     this._dates = [];
                     this._datesFormatted = [];
                 } else {
-                    outpValue = `${this._element.data('date')},`;
-                    outpValue = outpValue.replace(`${oldDate.format(this.actualFormat)},`, '').replace(',,', '').replace(/,\s*$/, '');
+                    outpValue = `${this._element.data('date')}${this._options.multidateSeparator}`;
+                    outpValue = outpValue.replace(
+                        `${oldDate.format(this.actualFormat)}${this._options.multidateSeparator}`, ''
+                    )
+                    .replace(`${this._options.multidateSeparator}${this._options.multidateSeparator}`, '')
+                    .replace(new RegExp(`${escapeRegExp(this._options.multidateSeparator)}\\s*$`), '');
                     this._dates.splice(index, 1);
                     this._datesFormatted.splice(index, 1);
                 }
+                outpValue = trim(outpValue);
                 if (this.input !== undefined) {
                     this.input.val(outpValue);
                     this.input.trigger('input');
@@ -461,10 +471,11 @@ const DateTimePicker = (($, moment) => {
                     for (let i = 0; i < this._dates.length; i++) {
                         outpValue += `${this._dates[i].format(this.actualFormat)}${this._options.multidateSeparator}`;
                     }
-                    outpValue = outpValue.replace(/,\s*$/, '');
+                    outpValue = outpValue.replace(new RegExp(`${this._options.multidateSeparator}\\s*$`), '');
                 } else {
                     outpValue = this._dates[index].format(this.actualFormat);
                 }
+                outpValue = trim(outpValue)
                 if (this.input !== undefined) {
                     this.input.val(outpValue);
                     this.input.trigger('input');
@@ -615,7 +626,7 @@ const DateTimePicker = (($, moment) => {
         }
 
         _isValid(targetMoment, granularity) {
-            if (!targetMoment.isValid()) {
+            if (!targetMoment || !targetMoment.isValid()) {
                 return false;
             }
             if (this._options.disabledDates && granularity === 'd' && this._isInDisabledDates(targetMoment)) {
@@ -783,7 +794,11 @@ const DateTimePicker = (($, moment) => {
         }
 
         _getLastPickedDate() {
-            return this._dates[this._getLastPickedDateIndex()];
+            let lastPickedDate = this._dates[this._getLastPickedDateIndex()];
+            if (!lastPickedDate && this._options.allowMultidate) {
+                lastPickedDate = moment(new Date());
+            }
+            return lastPickedDate;
         }
 
         _getLastPickedDateIndex() {
@@ -1499,8 +1514,8 @@ const DateTimePicker = (($, moment) => {
                 return this._options.multidateSeparator;
             }
 
-            if (typeof multidateSeparator !== 'string' || multidateSeparator.length > 1) {
-                throw new TypeError('multidateSeparator expects a single character string parameter');
+            if (typeof multidateSeparator !== 'string') {
+                throw new TypeError('multidateSeparator expects a string parameter');
             }
 
             this._options.multidateSeparator = multidateSeparator;