Missing vocative in first declension

[jk0592]

In Pharr, the paradigm for nouns of the first declension ending in α, such as θάλλασσα, are shown without giving the singular vocative.
This makes memorizing the declension difficult, since it does not contain the same number of elements as for the other paradigms,
which contain all the NGDAV cases.
So, is the missing vocative really absent in Homer, or is there another reason ?

[GlottalGreekGeek]

That is a typo. It should say "N. V." instead of merely "N", since in the declension of θάλλασσα the nominative and vocative are identical.

Though vocatives are not as common as, say, subjunctives, in Homeric or other Greek.