bug: AppConfig empty hosted configuration upload causes None.read() InternalError

[AndreKurait]

Reproduced on unmodified localstack/localstack-pro:dev, freshly pulled on 2026-10-10, native linux/amd64:

• Manifest sha256:513f218caf22d1fcb115f055225c96c7140813efcb23e48c9e24b688cdb31cd4
• Image sha256:b104c9b43442fba4e1e00ab68c447681b08db6dc6128273d105e1db5c87e5ab3
• Version 2026.10.0.dev97; SERVICES=appconfig; no extensions, source mounts, or custom entrypoint.

Uploading a zero-byte hosted configuration with ContentType=application/octet-stream returns HTTP 500 InternalError:

exception while calling appconfig.CreateHostedConfigurationVersion: 'NoneType' object has no attribute 'read'

Expected: either accept the zero-byte content if supported, or reject it with the appropriate modeled client error. A supplied empty payload should not cause an internal None.read() exception. I have not tested the empty-payload acceptance contract against AWS.

Minimal reproduction against a disposable LocalStack instance:

import uuid
import boto3
from botocore.config import Config

client = boto3.client(
    "appconfig", endpoint_url="http://localhost:4566", region_name="us-east-1",
    aws_access_key_id="000000000000", aws_secret_access_key="test",
    config=Config(retries={"max_attempts": 0}),
)
name = "appconfig-repro-" + uuid.uuid4().hex[:8]
app = client.create_application(Name=name)["Id"]
profile = client.create_configuration_profile(
    ApplicationId=app, Name="config", LocationUri="hosted", Type="AWS.Freeform",
)["Id"]
client.create_hosted_configuration_version(
    ApplicationId=app, ConfigurationProfileId=profile,
    Content=b"", ContentType="application/octet-stream",
)

A nonempty JSON upload to the same profile succeeds. The test used real boto3 requests with retries disabled. Fixture resources and the disposable container were cleaned up; no production AWS execution is claimed.

[AndreKurait]

Retested on 2026-10-10 against unmodified localstack/localstack-pro:dev, reporting Pro 2026.10.0.dev101 on Linux x86_64. This still reproduces.

Creating a hosted configuration version with an empty body still returns HTTP 500 / InternalError: exception while calling appconfig.CreateHostedConfigurationVersion: 'NoneType' object has no attribute 'read'.

Resolved image index: sha256:a9b3e374db5310d706c6676a498f22b2b33a45a110ec79dbd7c41f07209c7e28; amd64 image ID: sha256:9581779d9198ddfa6f1a300760edaf7f28052eb2cfdd8f713bb528b186e0cbcc. Public SDK requests only, with no source patches or extensions. Disposable resources and the container were cleaned up afterward.

[ryan-berke]

Hi @AndreKurait, thanks for being proactive with this issue. I have reproduced it on my side and escalated to my engineers for a fix. We will let you know once a fix is live for you to test. Thanks again!