fix: raise ValueError when no valid estimand is identified instead of silent None return

[abhiprd2000]

Summary

estimate_effect() silently returns None when identified_estimand.estimands[identifier_name] is None, logging an error but not raising. Users get no indication that identification failed.

Fix

Replace the silent return CausalEstimate(None, ...) with raise ValueError(error_msg) including the identifier name for easier debugging.

Impact

• callers now get a clear ValueError instead of silent None
• error message includes the identifier name to help users debug their graph or method choice
• adds a regression test to prevent future recurrence

Fixes #1551
Signed-off-by: abhiprd2000

[abhiprd2000]

Hi @emrekiciman,

follow-up to your suggestion on #1520. Fix and regression test included.

[abhiprd2000]

Hi @emrekiciman,

Noticed github-actions bot also filed a draft #1554 for the same fix. Mine includes an end-to-end test via CausalModel as we discussed in #1520. Happy to adjust anything if needed.

[Copilot]

Pull request overview

This PR makes estimate_effect() fail loudly when identification did not produce a valid estimand for the requested identifier, by raising a ValueError instead of returning a CausalEstimate with a None value. This aligns behavior with the expectation that a missing estimand indicates identification failure rather than a valid “no effect” result.

Changes:

• Raise a ValueError (with identifier name included) when identified_estimand.estimands[identifier_name] is None.
• Add a regression test covering the missing-estimand case for iv.instrumental_variable.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
dowhy/causal_estimator.py	Replaces the silent CausalEstimate(None, …) return with a logged ValueError when the estimand is missing.
tests/test_causal_estimator.py	Adds a regression test asserting estimate_effect() raises ValueError for missing IV estimand.

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[amit-sharma]

thanks @abhiprd2000 This looks good

[amit-sharma]

@all-contributors add @abhiprd2000 for code

[allcontributors]

@amit-sharma

I've put up a pull request to add @abhiprd2000! 🎉