php array_unique method "puts key into array" -

im going parse json array unique values. here problem array_unique function. example:

$contract_types = [ "asset sale , purchase agreement", "asset sale , purchase agreement", "concession agreement" ]; 

and

return array_unique($contract_types); 

gives me: [{ "0": "asset sale , purchase agreement", "2": "concession agreement" }]

what i'm doing wrong?

array_unique() preserves keys. php docs:

note keys preserved.

if wish reindex array has consecutive integer indexes, use array_values():

return array_values(array_unique($contract_types));