fix inverting of split_node and merge_node operations

packages/slate/src/changes/by-key.js

@@ -186,6 +186,7 @@ Changes.mergeNodeByKey = (change, key, options = {}) => {
     value,
     path,
     position,
+    target: null,
   })
 
   if (normalize) {

packages/slate/src/constants/operation-attributes.js

@@ -29,6 +29,7 @@ const OPERATION_ATTRIBUTES = {
     'value',
     'path',
     'position',
+    'target',
   ],
   move_node: [
     'value',

packages/slate/src/models/operation.js

@@ -104,7 +104,6 @@ class Operation extends Record(DEFAULTS) {
         if (key == 'document') continue
         if (key == 'selection') continue
         if (key == 'node' && type != 'insert_node') continue
-        if (key == 'target' && type == 'split_node') continue
 
         throw new Error(`\`Operation.fromJSON\` was passed a "${type}" operation without the required "${key}" attribute.`)
       }
@@ -224,7 +223,6 @@ class Operation extends Record(DEFAULTS) {
       if (key == 'selection') continue
       if (key == 'value') continue
       if (key == 'node' && type != 'insert_node') continue
-      if (key == 'target' && type == 'split_node') continue
 
       if (key == 'mark' || key == 'marks' || key == 'node') {
         value = value.toJSON()