Reverse for 'step' with arguments '()' and keyword arguments '{u'course_pk': 1, u'step_pk': ''}' not found

As per the video presentation, when editied course_detail.html with below lines and tried to access below link. Getting this error:

    <h3>
        <a href="{% url 'step' course_pk=step.course.pk step_pk=step_pk %}">{{ step.title }}</a>
    </h3>

http://10.32.12.14:8000/courses/1/

NoReverseMatch at /courses/1/ Reverse for 'step' with arguments '()' and keyword arguments '{u'course_pk': 1, u'step_pk': ''}' not found. 1 pattern(s) tried: ['courses/(?P<course_pk>\d+)/(?P<step_pk>\d+)/$'] Request Method: GET Request URL: http://10.32.12.14:8000/courses/1/ Django Version: 1.9.13 Exception Type: NoReverseMatch Exception Value:
Reverse for 'step' with arguments '()' and keyword arguments '{u'course_pk': 1, u'step_pk': ''}' not found. 1 pattern(s) tried: ['courses/(?P<course_pk>\d+)/(?P<step_pk>\d+)/$'] Exception Location: /usr/local/lib/python2.7/dist-packages/django/core/urlresolvers.py in _reverse_with_prefix, line 508 Python Executable: /usr/bin/python Python Version: 2.7.6 Python Path:
['/root/Django/learning_site', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-x86_64-linux-gnu', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages']