stock held on 30.6.17 with Nil input credit

Have a look at both of the following articles, You will get an answer for your query

Link 1 :/articles/the-biggest-question-what-to-do-of-stock-on-30th-june--30344.asp

Link 2:/articles/gst-impact-on-stock-available-till-30th-june--30370.asp

If You can't opt Composition scheme in below mentioned cases

1) Goods purchased from other state still availble in stock

2) Before opt Compostion scheme you pay tax on those goods which was purchased from Non registered dealer in Old Tax Law