doctests are failing with opencv 3

OpenCV Error: Assertion failed (!empty()) in detectMultiScale, file /feedstock_root/build_artefacts/work/opencv-3.1.0/modules/objdetect/src/cascadedetect.cpp, line 1639
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File "guide.rst", line 64, in default
Failed example:
    try:
      from cv2 import CascadeClassifier
      cc = CascadeClassifier(get_file('haarcascade_frontalface_alt.xml'))
      face_bbxs = cc.detectMultiScale(lena_gray, 1.3, 4, 0, (20, 20))
    except ImportError: #if you don't have OpenCV, do it otherwise
      face_bbxs = [[214, 202, 183, 183]] #e.g., manually
Exception raised:
    Traceback (most recent call last):
      File "/local/conda/envs/bob-devel-py27/lib/python2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest default[4]>", line 4, in <module>
        face_bbxs = cc.detectMultiScale(lena_gray, 1.3, 4, 0, (20, 20))
    error: /feedstock_root/build_artefacts/work/opencv-3.1.0/modules/objdetect/src/cascadedetect.cpp:1639: error: (-215) !empty() in function detectMultiScale

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File "guide.rst", line 70, in default
Failed example:
    print(face_bbxs)
Exception raised:
    Traceback (most recent call last):
      File "/local/conda/envs/bob-devel-py27/lib/python2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest default[5]>", line 1, in <module>
        print(face_bbxs)
    NameError: name 'face_bbxs' is not defined
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File "guide.rst", line 86, in default
Failed example:
    x, y, width, height = face_bbxs[0]
Exception raised:
    Traceback (most recent call last):
      File "/local/conda/envs/bob-devel-py27/lib/python2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest default[0]>", line 1, in <module>
        x, y, width, height = face_bbxs[0]
    NameError: name 'face_bbxs' is not defined
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File "guide.rst", line 89, in default
Failed example:
    keypoints = localizer.locate(lena_gray, y, x, height, width)
Exception raised:
    Traceback (most recent call last):
      File "/local/conda/envs/bob-devel-py27/lib/python2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest default[3]>", line 1, in <module>
        keypoints = localizer.locate(lena_gray, y, x, height, width)
    NameError: name 'y' is not defined
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File "guide.rst", line 90, in default
Failed example:
    keypoints
Exception raised:
    Traceback (most recent call last):
      File "/local/conda/envs/bob-devel-py27/lib/python2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest default[4]>", line 1, in <module>
        keypoints
    NameError: name 'keypoints' is not defined
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1 items had failures:
   5 of  11 in default
11 tests in 1 items.
6 passed and 5 failed.
***Test Failed*** 5 failures.