An unattended backpack found in front of City Hall in Jersey City Sunday night drew a quick response from police, who discovered that it was harmless, authorities said. The call for 280 Grove St. came in at 8:40 p.m. Upon investigation by the Jersey City Police Department Bomb Squad, it was determined that the backpack contained clothing and miscellaneous garbage, city spokeswoman Kimberly Wallace-Scalcione said. No hazardous items were encountered.