BUG: Stairs._has_na fails when Stairs._data is None or does not contain a "value" column

[venaturum]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of staircase.

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Problem description

staircase/staircase/core/stairs.py

Line 81 in cb0265d

def _has_na(self):

This is a "private" function which checks to see if there are any undefined areas of the step function.

Test optional