fix: fix error when previewing attachment on outlook.office.com

this fix guards against edge cases where the contentEditable being monitored does not have an
offsetParent, which can happen if the node has position of 'fixed'.

fixes #141

spec/JustNotSorrySpec.test.js

@@ -147,6 +147,32 @@ describe('JustNotSorry', () => {
       expect(wrapper.state('parentNode')).toBe(domNode.parentNode);
     });
 
+    describe('when the email node is null', () => {
+      it('clears the state', () => {
+        instance.updateWarnings(null, [
+          buildWarning('\\b!{3,}\\B', 'warning message'),
+        ]);
+
+        expect(wrapper.state('warnings').length).toEqual(0);
+        expect(wrapper.state('parentNode')).toEqual({});
+      });
+    });
+
+    describe('when the email node has an offsetParent of null', () => {
+      it('clears the state', () => {
+        const emailNode = {
+          offsetParent: null,
+          childNodes: [],
+        };
+        instance.updateWarnings(emailNode, [
+          buildWarning('\\b!{3,}\\B', 'warning message'),
+        ]);
+
+        expect(wrapper.state('warnings').length).toEqual(0);
+        expect(wrapper.state('parentNode')).toEqual({});
+      });
+    });
+
     describe('when there are top-level and child nodes', () => {
       it('catches the warnings for both', () => {
         const elem = mount(

src/components/JustNotSorry.js

@@ -42,6 +42,10 @@ class JustNotSorry extends Component {
   }
 
   updateWarnings(email, patterns) {
+    if (!email || !email.offsetParent) {
+      this.resetState();
+      return;
+    }
     const newWarnings =
       email.childNodes.length > 0
         ? Array.from(email.childNodes)