LUT Descriptor tag with no value yields TypeError

[deeuu]

Describe the bug
I have a DICOM image with the following tag (copied from ImageJ)

0028,1101  Red Palette Color Lookup Table Descriptor: 

which corresponds to the raw data element, produced by DataElement_from_raw:

RawDataElement(tag=(0028, 1101), VR='US', length=0, value=None, value_tell=1850, is_implicit_VR=False, is_little_endian=True)

Because this tag is matched by the LUT Descriptor tags and the value is empty (None), the following line:

if raw.tag in _LUT_DESCRIPTOR_TAGS and value[0] < 0:

results in

TypeError: 'NoneType' object is not subscriptable

Expected behavior

Given that I discovered this by parsing what seems to be a set of faulty DICOMs (mangled pixel data), I'm not sure if an error should be raised if the colour attribute value is not provided.

However, given that value can be None for other tags, the simple fix is

try:
    if raw.tag in _LUT_DESCRIPTOR_TAGS and value[0] < 0:
        # We only fix the first value as the third value is 8 or 16
        value[0] += 65536
except TypeError:
    pass

(or test if value is iterable).

Your environment

Darwin-19.3.0-x86_64-i386-64bit
Python  3.7.6 | packaged by conda-forge | (default, Jan  7 2020, 22:05:27)
[Clang 9.0.1 ]
pydicom  1.4.1

Many thanks!

[scaramallion]

LUT Descriptor and the Red/Green/Blue Palette Color LUT Descriptor elements are all type 1 or 1C, so nope they're not supposed to be empty. But I should've known better than to assume conformance...

Anyway, thanks! It'll be fixed soon.

[deeuu]

Excellent, thank you!

[scaramallion]

You can also workaround the issue by deleting the element before doing anything else:

ds = dcmread('filename.dcm')
del ds[0x00281101]