I use the {1} here to emulate the behaviour of an e match. Perhaps theres a better way, if so let me know.

Just use nothing.

expr      :     term expr_tail
expr_tail : '+' term expr_tail |
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or

expr      :     term expr_tail
expr_tail : '+' term expr_tail
          |
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or a comment

expr      :     term expr_tail
expr_tail : '+' term expr_tail
          | # Nothing
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or an empty rule

expr      :     term expr_tail
expr_tail : '+' term expr_tail
          | Epsilon

Epsilon   :
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