Universal 1164:

Original: … vocatives do not undergo definitization in any language investigated. Most vocatives take no article at all or take the definite article.
Standardized: Vocative nouns (or NPs) take no article or only the definite article, never the indefinite article.
Keywords: vocative, definite article
Domain: inflection, syntax
Type: unconditional
Status: achronic
Quality: absolute
Basis: 106 languages surveyed in Moravcsik 1969
Source: Moravcsik 1969: 72

FP