When response is null, status is set to 0, but the subsequent logic continues to check specific status codes and may attempt to extract error fields from the null response. Consider adding an early return or throwing an exception when response is null, or ensure that all downstream methods like extractErrorFields() handle null responses gracefully.

The null check for response is repeated multiple times in this method. Since the response is checked at line 622 and subsequent logic depends on it being non-null (line 624 throws an exception for STATUS_NOT_FOUND), the additional null checks at lines 651, 663 become redundant. Consider adding a single null check early in the method or documenting why response could legitimately be null at these points despite earlier checks.

The location and cookies variables are marked as final but their values are only used after the response null check. Since they're declared final, consider moving the declarations inside the null check block or removing the final modifier if they need to be conditionally initialized.

When response is null, location will be null (line 1517), leading to this exception being thrown. However, the error message 'transaction open failed to provide location' is misleading when the actual issue is a null response. Consider checking for null response explicitly before this line and providing a more accurate error message.

The condition 'body != null && body.contentLength() != 0' is repeated in multiple locations (lines 664, 927, 2586, 4846, 5065). Consider extracting this logic into a helper method like 'hasContent(ResponseBody body)' to improve maintainability and ensure consistency.

The comment expresses uncertainty about when serializedContent can be null ('Not sure if the doc can have null content'). This uncertainty should be resolved through code analysis or documentation review. Update the comment to either explain the specific scenarios where null content occurs or remove the speculative language if the behavior is now understood.