Fix KeyError for SVG without xmlns tag
Some SVG optimizers remove the xmlns
tag.
When retrieving metadata for SVG files, the parser wants to remove the Xmlns
key from the dict if it is the valid value. However, it sets the default value of the get
method to the valid value, so it will try to remove the key even if it doesn't exists, throwing an unhandled KeyError
value.
This MR removes the default value of the get
method so that the parser doesn't try to remove the Xmlns
key with SVG files without the xmlns
tag.