Count employees per department, including empty departments

Tables:

department(id int primary key, name text)

employee(id int primary key, department_id int) (department_id can be NULL)

Return every department with its number of employees, including departments with none (count 0).

Output columns: name, employee_count. Two departments can share a name, so they must stay separate rows.

CREATE TABLE department (
  id int PRIMARY KEY,
  name text NOT NULL
);
CREATE TABLE employee (
  id int PRIMARY KEY,
  department_id int
);