Adds check to ensure that Tulsi was found.
Adds check to ensure that Tulsi was found.

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MOS_MIGRATED_REVID=115259589

bazelbuild/tulsi,pinterest/tulsi,pinterest/tulsi,pinterest/tulsi,bazelbuild/tulsi,pinterest/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,pinterest/tulsi,pinterest/tulsi