Add checks and guards for nullable and unknown values

Author: acusti

src/component/handlers/edit/editOnBlur.js

@@ -28,7 +28,9 @@ function editOnBlur(editor: DraftEditor, e: SyntheticEvent): void {
   // issue to be certain, checking whether the active element is `body`
   // to force it when blurring occurs within the window (as opposed to
   // clicking to another tab or window).
-  var doc = e.target && e.target.ownerDocument || document;
+  var doc = e.target && e.target.ownerDocument instanceof Document ?
+      e.target.ownerDocument :
+      document;
   var activeElement = getActiveElement(doc);
   if (isWebKit && activeElement === doc.body) {
     doc.defaultView.getSelection().removeAllRanges();

src/component/selection/getDraftEditorSelectionWithNodes.js

@@ -155,8 +155,9 @@ function getPointForNonTextNode(
   // wrapper.
   if (editorRoot === node) {
     node = node.firstChild;
+    var win = node && node.ownerDocument.defaultView;
     invariant(
-      node instanceof node.ownerDocument.defaultView.Element && node.getAttribute('data-contents') === 'true',
+      win && node instanceof win.Element && node.getAttribute('data-contents') === 'true',
       'Invalid DraftEditorContents structure.',
     );
     if (childOffset > 0) {

src/component/selection/getSelectionOffsetKeyForNode.js

@@ -19,7 +19,7 @@
  */
 function getSelectionOffsetKeyForNode(node: Node): ?string {
   var win = node.ownerDocument.defaultView;
-  if (node instanceof win.Element) {
+  if (win && node instanceof win.Element) {
     var offsetKey = node.getAttribute('data-offset-key');
     if (offsetKey) {
       return offsetKey;

src/model/encoding/convertFromHTMLToContentBlocks.js

@@ -231,7 +231,7 @@ function processInlineTag(
   currentStyle: DraftInlineStyle,
 ): DraftInlineStyle {
   var styleToCheck = inlineTags[tag];
-  var win = node.ownerDocument.defaultView;
+  var win = node.ownerDocument.defaultView || window;
   if (styleToCheck) {
     currentStyle = currentStyle.add(styleToCheck).toOrderedSet();
   } else if (node instanceof win.HTMLElement) {
@@ -318,7 +318,7 @@ function containsSemanticBlockMarkup(
 }
 
 function hasValidLinkText(link: Node): boolean {
-  const win = link.ownerDocument.defaultView;
+  const win = link.ownerDocument.defaultView || window;
   invariant(
     link instanceof win.HTMLAnchorElement,
     'Link must be an HTMLAnchorElement.',
@@ -359,7 +359,7 @@ function genFragment(
       text = text.replace(REGEX_LF, SPACE);
     }
 
-    // save the last block so we can use it later
+    // Save the last block so we can use it later
     lastBlock = nodeName;
 
     return {
@@ -373,7 +373,7 @@ function genFragment(
     };
   }
 
-  // save the last block so we can use it later
+  // Save the last block so we can use it later
   lastBlock = nodeName;
 
   // BR tags
@@ -390,7 +390,7 @@ function genFragment(
     return {chunk: getSoftNewlineChunk(), entityMap};
   }
 
-  const win = node.ownerDocument.defaultView;
+  const win = node.ownerDocument.defaultView || window;
 
   // IMG tags
   if (