Fix issue when a nested in mark node a "void" inline node is the cause of error in applyMark method (#1831)

packages/slate-html-serializer/src/index.js

@@ -299,7 +299,7 @@ class Html {
           leaf.marks.push({ type, data })
           return leaf
         })
-      } else {
+      } else if (node.nodes) {
         node.nodes = node.nodes.map(applyMark)
       }
 

packages/slate-html-serializer/test/deserialize/mark-void-inline.js

@@ -0,0 +1,53 @@
+/** @jsx h */
+
+import h from '../helpers/h'
+
+export const config = {
+  rules: [
+    {
+      deserialize(el, next) {
+        switch (el.tagName.toLowerCase()) {
+          case 'p': {
+            return {
+              object: 'block',
+              type: 'paragraph',
+              nodes: next(el.childNodes),
+            }
+          }
+          case 'strong': {
+            return {
+              object: 'mark',
+              type: 'bold',
+              nodes: next(el.childNodes),
+            }
+          }
+          case 'br': {
+            return {
+              object: 'inline',
+              type: 'linebreak',
+              isVoid: true,
+            }
+          }
+        }
+      },
+    },
+  ],
+}
+
+export const input = `
+<p><strong>one<br/>two</strong></p>
+`.trim()
+
+export const output = (
+  <value>
+    <document>
+      <paragraph>
+        <b>
+          one
+          <linebreak />
+          two
+        </b>
+      </paragraph>
+    </document>
+  </value>
+)

packages/slate-html-serializer/test/helpers/h.js

@@ -25,6 +25,10 @@ const h = createHyperscript({
       type: 'emoji',
       isVoid: true,
     },
+    linebreak: {
+      type: 'linebreak',
+      isVoid: true,
+    },
   },
   marks: {
     b: 'bold',