Nightingale

4 lines

This hanjie is a linea, that means:
Each black box has exactly two black direct neighboring boxes, except for the two "ends" which have only one black direct neighboring box.
We cannot therefore have either squares of four black squares, nor "T" (not allowed: ├ ┬ ├ ┴ ■ )
Warning: sometimes a linea may not be logical as an hanjie, but only if we add the constraint described above.