Allow null as transactions errors value

index.bs

@@ -947,8 +947,12 @@ which is an [=/event loop=].
 A [=/transaction=] has a <dfn>request list</dfn> of pending [=/requests=]
 which have been made against the transaction.
 
-A [=/transaction=] has a <dfn>error</dfn> which is set if the
-[=/transaction=] is [=transaction/aborted=].
+A [=/transaction=] has a <dfn>error</dfn> which is set if the [=/transaction=] is [=transaction/aborted=].
+
+<div class=note>
+  <span class=marker>NOTE:</span>
+  Implementors need to keep in mind that the value "null" is considered an error, as it is set from {{IDBTransaction/abort()}}
+</div>
 
 A [=/transaction=]'s [=get the parent=] algorithm returns the
 transaction's [=transaction/connection=].
@@ -5214,6 +5218,8 @@ To <dfn>commit a transaction</dfn> with the |transaction| to commit, run these s
 
 To <dfn>abort a transaction</dfn> with the |transaction| to abort, and |error|, run these steps:
 
+1. If [=transaction/state=] is [=transaction/finished=], abort these steps.
+
 1. All the changes made to the [=/database=] by the [=/transaction=]
     are reverted. For [=/upgrade transactions=] this includes changes
     to the set of [=/object stores=] and [=/indexes=], as well as the
@@ -5231,8 +5237,7 @@ To <dfn>abort a transaction</dfn> with the |transaction| to abort, and |error|,
 
 1. Set |transaction|'s [=transaction/state=] to [=transaction/finished=].
 
-1. If |error| is not null, set |transaction|'s
-    [=transaction/error=] to |error|.
+1. Set |transaction|'s [=transaction/error=] to |error|.
 
 1. [=list/For each=] |request| of |transaction|'s [=transaction/request list=],
     abort the steps to [=asynchronously execute a request=] for |request|,
@@ -6885,6 +6890,7 @@ For the revision history of the second edition, see [that document's Revision Hi
 * Add {{IDBObjectStore/getAllRecords(options)}} method to {{IDBObjectStore}} and {{IDBIndex}}. (<#206>)
 * Add direction option to {{IDBObjectStore/getAll()}} and {{IDBObjectStore/getAllKeys()}} for {{IDBObjectStore}} and {{IDBIndex}} (<#130>)
 * Use of {{QuotaExceededError}} has been updated to reflect that it is now a {{DOMException}}-derived interface instead of an exception name. (<#463>)
+* Specify that null is valid for [=transaction/error=], and allow it to be set in [=abort a transaction=] (<#433>)
 
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 # Acknowledgements # {#acknowledgements}