With occupations and similar, you don’t use the indefinite article.
- Hon är advokat. (She’s a lawyer.)
- Han är lärare. (He’s a teacher.)
- Han är rasist. (He’s a racist.)
French is the same way, and the French word for lawyer is un avocat or une avocate. Does anyone know if this is coincidental or not?
It’s the same in German and Spanish as well, not sure what the reason behind it is or why English differs. The word itself is borrowed from Latin.
Probably has to do with the root word in "advocate" - another term for a lawyer. Lawyers advocate for their clients.