Don't try to store POST data for a nil CWRSessionEntry

ios/web/web_state/ui/crw_web_controller.mm

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/web_state/ui/crw_web_controller.h"
 
 #import <objc/runtime.h>
 #include <stddef.h>
 #include <cmath>
 
@@ skipping 2801 matching lines @@
       // Record the URL so that errors reported following the 'NO' reply can be
       // safely ignored.
       [_openedApplicationURL addObject:request.URL];
       if ([self shouldClosePageOnNativeApplicationLoad])
         [_delegate webPageOrderedClose];
     }
     return NO;
   }
 
   if ([[request HTTPMethod] isEqualToString:@"POST"]) {
-    [self cachePOSTDataForRequest:request
-                   inSessionEntry:[self currentSessionEntry]];
+    CRWSessionEntry* currentEntry = [self currentSessionEntry];
+    // TODO(crbug.com/570699): Remove this check once it's no longer possible to
+    // have no current entries.
+    if (currentEntry)
+      [self cachePOSTDataForRequest:request inSessionEntry:currentEntry];
   }
 
   return YES;
 }
 
 - (void)restoreStateAfterURLRejection {
   [[self sessionController] discardNonCommittedEntries];
 
   // Reset |_lastRegisteredRequestURL| so that it reflects the URL from before
   // the load was rejected. This value may be out of sync because
@@ skipping 1061 matching lines @@
   if ([MIMEType isEqualToString:@"text/html"] ||
       [MIMEType isEqualToString:@"application/xhtml+xml"] ||
       [MIMEType isEqualToString:@"application/xml"]) {
     return web::WEB_VIEW_DOCUMENT_TYPE_HTML;
   }
 
   return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
 }
 
 @end