There are three different dichloroethylenes (molecular formula C₂H₂Cl₂), which we can designate X, Y, and Z. Compound X has no dipole moment, but compound Z does. Compounds X and Z each combine with hydrogen to give the same product:
C₂H₂Cl₂(X or Z) + H₂ → ClCH₂ - CH₂Cl
What are the structures of X, Y, and Z? Would you expect compound Y to have a dipole moment?