Every registered taxable person is required to file returns under the GST law. If you have not performed any business activities during the period covered by a return, you need to file a Nil return.
There are some entities that will need to register for GST but aren’t required to file returns regularly, such as UN bodies (and foreign consulates) must register for a unique GST ID, but they are required to file returns only for months during which they make purchases.
Some entities do not need to register or file returns. Government entities and Public Sector Undertakings (PSUs), entities dealing with non-GST supplies, and those who deal with exempted/Nil rated/non GST goods and/or services will neither be required to register under the GST nor file returns.