fix(rest): handle empty body in AWS SigV4 signing

Author: plusplusjiajia

pyiceberg/catalog/rest/__init__.py

@@ -560,7 +560,14 @@ def add_headers(self, request: PreparedRequest, **kwargs: Any) -> None:  # pylin
                 params = dict(parse.parse_qsl(query))
 
                 # remove the connection header as it will be updated after signing
-                del request.headers["connection"]
+                if "connection" in request.headers:
+                    del request.headers["connection"]
+                # For empty bodies, explicitly set the content hash header to the SHA256 of an empty string
+                body = request.body
+                if body in (None, b"", ""):
+                    request.headers["x-amz-content-sha256"] = (
+                    "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+                )
 
                 aws_request = AWSRequest(
                     method=request.method, url=url, params=params, data=request.body, headers=dict(request.headers)