fix: Explicitly handle null attribute values (#1157)

* fix: Explicitly handle removed attributes

The attribute `value` can be null when a mutation observer triggers due to a removed attribute. This is currently not reflected by types and code.

* Apply formatting changes

* fix

* add changeset

packages/rrweb-snapshot/src/rebuild.ts

@@ -149,7 +149,7 @@ function buildNode(
        * They often overwrite other attributes on the element.
        * We need to parse them last so they can overwrite conflicting attributes.
        */
-      const specialAttributes: attributes = {};
+      const specialAttributes: { [key: string]: string | number } = {};
       for (const name in n.attributes) {
         if (!Object.prototype.hasOwnProperty.call(n.attributes, name)) {
           continue;
@@ -165,6 +165,11 @@ function buildNode(
           continue;
         }
 
+        // null values mean the attribute was removed
+        if (value === null) {
+          continue;
+        }
+
         /**
          * Boolean attributes are considered to be true if they're present on the element at all.
          * We should set value to the empty string ("") or the attribute's name, with no leading or trailing whitespace.