S3 get_bucket_location returns us-east-1 rather than None

In AWS, us-east-1 is the default region and as such, things behave a little bit differently there:

When a bucket is in us-east-1, it returns a LocationConstraint equal to None. moto returns us-east-1

In [9]: s3_cli.get_bucket_location(Bucket='pix4d-development-us-east-1-assets-drop-zone')
Out[9]:
{'ResponseMetadata': {'RequestId': 'D6CC81F0D293872E',
  'HostId': 'LCf3LHvjW0lpzZ81YTsZYdU33hwqr3HeBm8pDvxEUArDwEZwA/zY38L84S9u8isM8bO3UcXH9H0=',
  'HTTPStatusCode': 200,
  'HTTPHeaders': {'x-amz-id-2': 'LCf3LHvjW0lpzZ81YTsZYdU33hwqr3HeBm8pDvxEUArDwEZwA/zY38L84S9u8isM8bO3UcXH9H0=',
   'x-amz-request-id': 'D6CC81F0D293872E',
   'date': 'Tue, 20 Nov 2018 07:17:41 GMT',
   'content-type': 'application/xml',
   'transfer-encoding': 'chunked',
   'server': 'AmazonS3'},
  'RetryAttempts': 0},
 'LocationConstraint': None}

Creating a bucket with CreateBucketConfiguration={'LocationConstraint': 'us-east-1'} should actually raise an error. Moto allows it.

In [7]: s3_cli.create_bucket(Bucket='pix4d-test-gba2', CreateBucketConfiguration={'LocationConstraint': 'us-east-1'})
...
ClientError: An error occurred (InvalidLocationConstraint) when calling the CreateBucket operation: The specified location-constraint is not valid

(this issue is somewhat related to #971)

getmoto / moto

S3 get_bucket_location returns us-east-1 rather than None #1959