Editorial: simplify session history serialized state

Previously, it could be either a serialized state or null. But, we treated null the same as the serialized form of null (i.e., StructuredSerializeForStorage(null)), when we deserialized it in "restore the history object state". This simplifies the infrastructure always having it be a serialized state, and never null.

Once this is done, it becomes clear that initializing new history entries with their serialized state set to StructuredSerializeForStorage(null) was pointless, since that is the default value. So, we can remove a couple instances of that.

source

@@ -86412,8 +86412,8 @@ interface <dfn interface>History</dfn> {
    methods that are invoked on a timer, or from event listeners that are not triggered in response
    to a clear user action, or that are invoked in rapid succession.)</p></li>
 
-   <li><p>Let <var>serializedData</var> be ?
-   <span>StructuredSerializeForStorage</span>(<var>data</var>).</p></li>
+   <li><p>Let <var>serializedData</var> be
+   <span>StructuredSerializeForStorage</span>(<var>data</var>). Rethrow any exceptions.</p></li>
 
    <li><p>Let <var>newURL</var> be <var>document</var>'s <span
    data-x="concept-document-url">URL</span>.</p></li>
@@ -88602,7 +88602,7 @@ interface <dfn interface>BeforeUnloadEvent</dfn> : <span>Event</span> {
    state</span>.</p></li>
 
    <li><p><dfn data-x="she-serialized-state">serialized state</dfn>, which is <span>serialized
-   state</span> or null, initially null.</p></li>
+   state</span>, initially <span>StructuredSerializeForStorage</span>(null).</p></li>
 
    <li><p><dfn data-x="she-scroll-restoration-mode">scroll restoration mode</dfn>, a <span>scroll
    restoration mode</span>, initially "<code
@@ -89999,9 +89999,6 @@ location.href = '#foo';</code></pre>
 
      <dt><span data-x="she-document-state">document state</span></dt>
      <dd><var>documentState</var></dd>
-
-     <dt><span data-x="she-serialized-state">serialized state</span></dt>
-     <dd><span>StructuredSerializeForStorage</span>(null)</dd>
     </dl>
 
     <p class="note">For the <span data-x="she-url">URL</span>, we do <em>not</em> use
@@ -90186,9 +90183,6 @@ location.href = '#foo';</code></pre>
      <dd><var>navigable</var>'s <span data-x="nav-active-history-entry">active session history
      entry</span>'s <span data-x="she-document-state">document state</span></dd>
 
-     <dt><span data-x="she-serialized-state">serialized state</span></dt>
-     <dd><span>StructuredSerializeForStorage</span>(null)</dd>
-
      <dt><span data-x="she-scroll-restoration-mode">scroll restoration mode</span></dt>
      <dd><var>navigable</var>'s <span data-x="nav-active-history-entry">active session history
      entry</span>'s <span data-x="she-scroll-restoration-mode">scroll restoration mode</span></dd>
@@ -91537,7 +91531,7 @@ location.href = '#foo';</code></pre>
      <li><p><span>Assert</span>: <var>locationURL</var> is a <span>URL</span>.</p></li>
 
      <li><p>Set <var>entry</var>'s <span data-x="she-serialized-state">serialized state</span> to
-     null.</p></li>
+     <span>StructuredSerializeForStorage</span>(null).</p></li>
 
      <li><p>Let <var>oldDocState</var> be <var>entry</var>'s <span
      data-x="she-document-state">document state</span>.</p></li>
@@ -92111,7 +92105,7 @@ location.href = '#foo';</code></pre>
         <p>If <var>targetEntry</var>'s <span data-x="she-document">document</span>'s <span
         data-x="concept-document-origin">origin</span> is not <var>oldOrigin</var>, then set
         <var>targetEntry</var>'s <span data-x="she-serialized-state">serialized state</span> to
-        null.</p>
+        <span>StructuredSerializeForStorage</span>(null).</p>
 
         <p class="note">This clears history state when the origin changed vs a previous load of
         <var>targetEntry</var> without a redirect occuring. This can happen due to a change in CSP
@@ -92696,12 +92690,9 @@ location.href = '#foo';</code></pre>
    <li><p>Let <var>targetRealm</var> be <var>document</var>'s <span
    data-x="concept-relevant-realm">relevant realm</span>.</p></li>
 
-   <li><p>Let <var>state</var> be null.</p></li>
-
-   <li><p>If <var>entry</var>'s <span data-x="she-serialized-state">serialized state</span> is not
-   null, then set <var>state</var> to <span>StructuredDeserialize</span>(<var>entry</var>'s <span
+   <li><p>Let <var>state</var> be <span>StructuredDeserialize</span>(<var>entry</var>'s <span
    data-x="she-serialized-state">serialized state</span>, <var>targetRealm</var>). If this throws
-   an exception, catch it and ignore the exception.</p></li>
+   an exception, catch it and let <var>state</var> be null.</p></li>
 
    <li><p>Set <var>document</var>'s <span data-x="doc-history">history object</span>'s <span
    data-x="concept-history-state">state</span> to <var>state</var>.</p></li>