diff --git a/sample/html/options.html b/sample/html/options.html
index 289e90a4..8f9855c3 100644
--- a/sample/html/options.html
+++ b/sample/html/options.html
@@ -68,7 +68,7 @@
     <article class="markdown-body entry-content">
         <div style="background-color: #f3f3f3; padding: 4px 20px 20px 20px;">
             <h4 style="color: #b94a48;">--Value</h4>
-            <label><input type="checkbox" id="strictMode">&nbsp;&nbsp;strictMode&nbsp;&nbsp;&nbsp;</label><br><br>
+            <label><input type="checkbox" id="strictMode" checked>&nbsp;&nbsp;strictMode=false&nbsp;&nbsp;&nbsp;</label><br><br>
             <label><input type="checkbox" id="defaultTag">&nbsp;&nbsp;defaultTag&nbsp;&nbsp;&nbsp;</label>
             <input type="text" id="defaultTag_value" placeholder="String ('p', 'div'..)"></input>
             <br><br>
@@ -609,7 +609,7 @@ <h2 class="sub-title">Applied options</h2>
     imageTable.innerHTML = '';
 
     var options = {
-        strictMode: document.getElementById('strictMode').checked ? true : undefined,
+        strictMode: document.getElementById('strictMode').checked ? undefined : false,
         defaultTag: document.getElementById('defaultTag').checked ? document.getElementById('defaultTag_value').value : undefined,
         textTags: document.getElementById('textTags').checked ? {
             bold: 'b',
diff --git a/src/lib/core.js b/src/lib/core.js
index d23ebdb6..1e8bfc01 100755
--- a/src/lib/core.js
+++ b/src/lib/core.js
@@ -6256,12 +6256,14 @@ export default function (context, pluginCallButtons, plugins, lang, options, _re
                 this._editorRange();
             }
 
-            if (util.isBreak(format.nextSibling)) util.removeItem(format.nextSibling);
-            if (util.isBreak(format.previousSibling)) util.removeItem(format.previousSibling);
-            if (util.isBreak(focusNode)) {
-                const zeroWidth = util.createTextNode(util.zeroWidthSpace);
-                focusNode.parentNode.insertBefore(zeroWidth, focusNode);
-                focusNode = zeroWidth;
+            if (format) {
+                if (util.isBreak(format.nextSibling)) util.removeItem(format.nextSibling);
+                if (util.isBreak(format.previousSibling)) util.removeItem(format.previousSibling);
+                if (util.isBreak(focusNode)) {
+                    const zeroWidth = util.createTextNode(util.zeroWidthSpace);
+                    focusNode.parentNode.insertBefore(zeroWidth, focusNode);
+                    focusNode = zeroWidth;
+                }
             }
 
             this.effectNode = null;