Under which condition does a reported null result provide robust evidence that the effect size is negligible?

Answer

If the null result originates from a study with high statistical power.

A null result from a well-powered experiment means the methodology was capable of detecting an effect if one existed; therefore, the result robustly supports the idea that the effect size is zero or negligible in that context.

Under which condition does a reported null result provide robust evidence that the effect size is negligible?
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