Client.Default - Null pointer exception when receiving an 'empty' response with compression

[TiagoCamilo]

Hello! Could you please evaluate the situation below and determine if it's necessary to implement an improvement?

When using Client.Default, and the server responds with:

• HTTP code: >= 400
• Header: Content-Encoding: gzip (or deflate)
• Body: "empty"

The following exception occurs:

java.lang.NullPointerException: null
	at java.base/java.util.zip.InflaterInputStream.<init>(InflaterInputStream.java:84) ~[na:na]
	at java.base/java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:77) ~[na:na]
	at java.base/java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:91) ~[na:na]
	at feign.Client$Default.convertResponse(Client.java:138) ~[feign-core-13.3.jar:na]
	at feign.Client$Default.execute(Client.java:107) ~[feign-core-13.3.jar:na]
	at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:100) ~[feign-core-13.3.jar:na]
	at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:70) ~[feign-core-13.3.jar:na]
	at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:99) ~[feign-core-13.3.jar:na]
	at com.example.feign_example.$Proxy63.test(Unknown Source) ~[na:na]

Below is an example of an endpoint that reproduces this response:

@PostMapping("/empty-body")
public ResponseEntity<byte[]> emptyBody() {
    HttpHeaders headers = new HttpHeaders();
    headers.add(HttpHeaders.CONTENT_ENCODING, "gzip");

    return ResponseEntity.status(HttpStatus.BAD_REQUEST).headers(headers).build();
}

In my opinion, the ideal result would be for a FeignException to occur with the HTTP code returned by the server, just as it does when the response body is not empty.