This is essentially the same as the whitespace effects you asked about in Whitespace effects in x+1 … Julia is sensitive to whitespace in some contexts, especially with the + operator (which can be either prefix or infix) and especially inside [...] brackets (which can be either comprensions or array literals, with special whitespace-based syntax for matrix literals).
It’s safer to give an error in cases where the parsing is ambiguous. That being said, the error message here could probably be clearer.
PS. See PSA: how to quote code with backticks … I’ve fixed it for you above.
PPS. I’ve edited your post title to make the subject of this thread clearer.