وَقَدْ يُحْذَفُ اسْمُ «لَا» لِقَرِينَةٍ، نَحْوُ: «لَا عَلَيْكَ»، أَيْ: لَا بَأْسَ عَلَيْكَ.
Translation: The noun of lā may be omitted when the context makes it clear; for instance lā ʿalayka means lā baʾsa ʿalayka (“No harm upon you”).
The book cites «لَا عَلَيْكَ» and explains it as «لَا بَأْسَ عَلَيْكَ» (“No harm is upon you”).
The noun of lā is absent in the surface wording but understood from context. This is ellipsis supported by context.
Do not freely supply an unexpressed noun where no contextual evidence supports it.