minimal fix to resolve #707

[ras44]

Proposed changes

This is a minimal fix to resolve the issue described in #707. The fix contains assertions in the functions get_cumlift, get_qini, get_tmlegain, and get_tmleqini that required columns in the dataframes do not contain null values. An example test for get_cumlift is included.

Types of changes

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• [X] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update (if none of the other choices apply)

Checklist

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• [X] I have read the CONTRIBUTING doc
• [X] I have signed the CLA
• [X] Lint and unit tests pass locally with my changes
• [X] I have added tests that prove my fix is effective or that my feature works
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Further comments

None

[ras44]

Let's merge this PR as is and open a new PR for adding an option for skipna=False. Thanks for the contribution.

Took a quick look at this and not sure how the skipna=False argument should work:

• the current assertions ensure that there are no NaNs in the required columns
• therefore calculating .cumsum(skipna) seems redundant since there never will be NaNs

https://github.com/uber/causalml/blob/d26e0891f3aa6279e359fe6abe1dd77e1f125c8a/causalml/metrics/visualize.py#L115C5-L115C5

Is the idea for skipna to allow NaN's in the dataframe? So:

• if skipna==True then
  • skip assertion check and calculate .cumsum(skipna)