UNIQUE constraint causes a query with string comparison to omit a row in the result set

Consider the following test case:

CREATE TABLE t0(c0 INT UNIQUE);

INSERT INTO t0 VALUES (NULL), (NULL), (NULL), (NULL), (1), (0);

SELECT * FROM t0 WHERE c0 < '\n2'; -- expected rows with c0=0 and c0=1, actual: only row with c0=0 is fetched

The query only fetches a single row. This is unexpected, because the expression in the WHERE clause evaluates to TRUE for two records:

SELECT c0 < '\n2' FROM t0; -- evaluates to TRUE for two rows

When removing the UNIQUE constraint from the column, or inserting fewer NULL values, the query works as expected.