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

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index 2dc4d955b92c5ef8a0e0bcdfe4b00db2c8204e27..4b1e6cbe77b0871fed6141881059cf73c84bc29c 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -2821,8 +2821,11 @@ const NSTimeInterval kSnapshotOverlayTransition = 0.5;
   }
 
   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;