Error opening Calendar View of Leads and Opportunities

[Andreas Brueckl]

OpenERP Version: openerp-7.0-20130630-231044.tar.gz
Linux: Ubuntu 12.04 LTS

When clicking onto calendar view in menu "Leads" or "Opportunities" I receive the following error.
The problem occurs even if there is no lead or opportunity at all.

Client Traceback (most recent call last):
  File "/opt/openerp/v7/openerp/addons/web/http.py", line 204, in dispatch
    response["result"] = method(self, **self.params)
  File "/opt/openerp/v7/openerp/addons/web/controllers/main.py", line 1051, in search_read
    return self.do_search_read(req, model, fields, offset, limit, domain, sort)
  File "/opt/openerp/v7/openerp/addons/web/controllers/main.py", line 1074, in do_search_read
    req.context)
  File "/opt/openerp/v7/openerp/addons/web/session.py", line 42, in proxy
    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)
  File "/opt/openerp/v7/openerp/addons/web/session.py", line 30, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/opt/openerp/v7/openerp/addons/web/session.py", line 103, in send
    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)

Server Traceback (most recent call last):
  File "/opt/openerp/v7/openerp/addons/web/session.py", line 89, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/opt/openerp/v7/openerp/netsvc.py", line 292, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/opt/openerp/v7/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/opt/openerp/v7/openerp/osv/osv.py", line 188, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/opt/openerp/v7/openerp/osv/osv.py", line 131, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/opt/openerp/v7/openerp/osv/osv.py", line 197, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/opt/openerp/v7/openerp/osv/osv.py", line 185, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/opt/openerp/v7/openerp/osv/orm.py", line 2354, in search
    return self._search(cr, user, args, offset=offset, limit=limit, order=order, context=context, count=count)
  File "/opt/openerp/v7/openerp/osv/orm.py", line 4845, in _search
    query = self._where_calc(cr, user, args, context=context)
  File "/opt/openerp/v7/openerp/osv/orm.py", line 4674, in _where_calc
    e = expression.expression(cr, user, domain, self, context)
  File "/opt/openerp/v7/openerp/osv/expression.py", line 640, in __init__
    self.parse(cr, uid, context=context)
  File "/opt/openerp/v7/openerp/osv/expression.py", line 757, in parse
    field_path = left.split('.', 1)
AttributeError: 'NoneType' object has no attribute 'split'