str(suds.sax.document.Document()) raises exception

If the Document object is created without a root element, its overridden version of __str__ throws an exception.

I encountered this bug with an interaction between the django debug toolbar and suds. In suds's suds.mx.core.append method, log.debug() can be called with a Document that has no children. Django's debug toolbar calls str() on the arguments to debug(), which causes the exception to be raised.

Reproduce:
import suds
str(suds.sax.document.Document())

Fix:
replace str and plain definitions in suds.sax.document.Document with the code below:
def str(self):
    s = []
    s.append(self.DECL)
    s.append('\n')
    root = self.root()
    if root is not None:
        s.append(root.str())
    return ''.join(s)

def plain(self):
    s = []
    s.append(self.DECL)
    root = self.root()
    if root is not None:
        s.append(root.plain())
    return ''.join(s)

Affects:
All versions of Ubuntu, all versions of suds