includes/class-freemius.php
function get_network_install_blog_id() {
            if ( ! $this->_is_network_active ) {
                return null;
            }

            return FS_Site::is_valid_id( $this->_storage->network_install_blog_id ) ?
                $this->_storage->network_install_blog_id :
                null;
        }
function get_network_install_blog_id() {
            if ( ! $this->_is_network_active ) {
                return null;
            }

            return FS_Site::is_valid_id( $this->_storage->network_install_blog_id ) ?
                $this->_storage->network_install_blog_id :
                null;
        }
function get_network_install_blog_id ( ) { if ( ! $ this -> _is_network_active ) { return null ; } return FS_Site :: is_valid_id ( $ this -> _storage -> network_install_blog_id ) ? $ this -> _storage -> network_install_blog_id : null ; }
Returns the blog ID that is associated with the main install.

@author Leo Fajardo (@leorw)
@since  2.0.0

@return int|null
Returns the blog ID that is associated with the main install .