Try listening to it on headphones (if you haven't already). I'm certain it's "not", you can definitely hear the 't' sound in the last line, but the point is Amy drops her T's sometimes when she's singing very softly because you don't want to accentuate a harsh sound like a letter T in a gentle song like that. It almost sounds like "goodnigh" rather than "goodnight" at the end, but nobody's arguing that one

This is a beautiful song. Sometimes when I can't sleep I sort of play it through in my head - it's very calming.

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