Try this:

    pts = {{}, {}, {{t1, a1, b1, c1}}, {}, {{ti, ai, bi, ci}}}
    
    (*  {{}, {}, {{t1, a1, b1, c1}}, {}, {{ti, ai, bi, ci}}}  *)
    
    pts /. {} -> Nothing
    
    (* {{{t1, a1, b1, c1}}, {{ti, ai, bi, ci}}}  *)

Have fun!