Conn.close() causes a panic when there is no valid connection

[brandon-langley-mf]

Mar 22 20:20:00.807275 ERROR driver: cannot connect to vertica-default.secopstn01.us-west-1.internal.mp.idi-dev.cyberreseng.com:5433 (dial tcp 10.35.87.182:5433: connect: connection refused)
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x7075e9]

goroutine 36 [running]:
database/sql.(*Conn).close(0x10?, {0x0?, 0x0?})
/usr/local/go/src/database/sql/sql.go:2108 +0x49
database/sql.(*Conn).Close(0xc000037b70?)
/usr/local/go/src/database/sql/sql.go:2129 +0x1d
main.(*vertica).CopyFilesFromS3(0xc000068820, {0xc00001e4c0, 0x1, 0x81c2bd?}, {0xc000258c00, 0x5b0}, 0xc000064100)
/src/vertica.go:144 +0x299
main.(*ingestor).ProcessBatch(0xc0000900e0, {0xc00009e3c0, 0x1, 0x1}, 0xc000064100)
/src/ingestor.go:94 +0x283
main.(*ingestor).Run(0xc0000900e0, 0x3)
/src/ingestor.go:55 +0x1b2
created by main.main
/src/main.go:92 +0x885