  We prove that if $K$ is a nontrivial null-homotopic knot in a closed oriented
$3$--manfiold $Y$ such that $Y-K$ does not have an $S^1\times S^2$ summand,
then the zero surgery on $K$ does not have an $S^1\times S^2$ summand. This
generalizes a result of Hom and Lidman, who proved the case when $Y$ is an
irreducible rational homology sphere.
