Condition at Inverse function

My goal is to get inverse of -Log[1 – x]. But the result shows conditional expression.
Could I know Why the condition -[Pi] <= Im[y] < [Pi] shows? There wass no assumption at variable y.

u[x_] := -Log[1 - x]

x /. Solve[y == u[x], x][[1]]

And the result showed,

ConditionalExpression[1 - E^-y, -[Pi] <= Im[y] < [Pi]]

u[x_] := -Log[1 - x]

Assuming[{Element[x, Reals], Element[y, Reals]}, x /. Solve[y == u[x], x][[1]]]

1 - E^-y