panic: panic: attempt to set nil err

[overstarry]

panic log:

panic: attempt to set nil err
goroutine 118194 [running]:
github.com/lib/pq.(*syncErr).set(0xc000065e20?, {0x0?, 0x0?})
/src/vendor/github.com/lib/pq/conn.go:195 +0xf8
github.com/lib/pq.(*conn).watchCancel.func2()
/src/vendor/github.com/lib/pq/conn_go18.go:133 +0xb8
github.com/lib/pq.(*conn).closeTxn(0xc000065e88?)
/src/vendor/github.com/lib/pq/conn.go:586 +0x23
github.com/lib/pq.(*conn).Rollback(0xc00022c600)
/src/vendor/github.com/lib/pq/conn.go:632 +0x102
database/sql.(*Tx).rollback.func1()
/usr/local/go/src/database/sql/sql.go:2322 +0x2f
database/sql.withLock({0x11a3ed8, 0xc000ff8480}, 0xc000b16f80)
/usr/local/go/src/database/sql/sql.go:3437 +0x8c
database/sql.(*Tx).rollback(0xc0017f7000?, 0x1)
/usr/local/go/src/database/sql/sql.go:2321 +0xc6
database/sql.(*Tx).awaitDone(0xc002b95c80)
/usr/local/go/src/database/sql/sql.go:2198 +0x45
created by database/sql.(*DB).beginDC
/usr/local/go/src/database/sql/sql.go:1903 +0x23b