title: Django: dependencies reference nonexistent parent node
body: <p>When I run the following command</p>
  
  <pre><code>python manage.py migrate
  </code></pre>
  
  <p>I receive this error from django so can't step forward in my practice:</p>
  
  <pre><code>Traceback (most recent call last):
    File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
      utility.execute()
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
      self.fetch_command(subcommand).run_from_argv(self.argv)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
      self.execute(*args, **options.__dict__)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
      output = self.handle(*args, **options)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 63, in handle
      executor = MigrationExecutor(connection, self.migration_progress_callback)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 17, in __init__
      self.loader = MigrationLoader(self.connection)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/db/migrations/loader.py", line 48, in __init__
      self.build_graph()
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/db/migrations/loader.py", line 241, in build_graph
      self.graph.add_dependency(migration, key, parent)
    File "/home/nikhil/testWeb-devEnv/local/lib/python2.7/site-packages/django/db/migrations/graph.py", line 42, in add_dependency
      raise KeyError("Migration %s dependencies reference nonexistent parent node %r" % (migration, parent))
  KeyError: u"Migration testBolt.0001_initial dependencies reference nonexistent parent node (u'delivery_boy', u'0004_auto_20150221_2011')"
  </code></pre>
  
  <p>How do I solve this problem?</p>