There is a "huge gap" in the history of Sikhism that needs to be filled, Urban Development Minister Hardeep Singh Puri said on Thursday as he released a book on Guru Tegh Bahadur, the ninth guru of the Sikhs. At the launch of academician Kuldeep Chand Agnihotri's book 'Shri Guru Tegh Bahadur', Puri said British Indian historiography was very "deficient".