Support `NULL` values for hstore keys

[acannistra]

Hstore columns that contain keys that map to NULL values cause the hstore parser to fail. The cause of the problem is that the string representation of the hstore that we're using does not place quotes (") around NULL values like it does with all other values (come to think of it, this might also happen with integer values.) The string parsing method we're using to parse keys and values out of the hstore string representation fails if there are NULL values without quotes, because the parser tries (and fails) to remove the quotes.

The problem code:

changegen/changegen/db.py

Lines 7 to 25 in fe32cc1

	def hstore_as_dict(hstore_str):
	"""
	Converts a string representation of a Postgres hstore
	into a Python dictionary. hstore strings should be
	of the form "'key1'=>'value1', "key2"=>"value2", ..."
	:param hstore_str: hstore string
	:type hstore_str: str
	:rtype: dict
	"""
	if len(hstore_str) > 0:
	return dict(
	map(
	lambda x: map(lambda x: x.strip().replace('"', ""), x.split("=>")),
	hstore_str.split('", '),
	)
	)
	else:
	return {}