Unable to add or modify foreign key

I am facing the same issue as mentioned here. But this time it is not ALTER TABLE which gives the error. It is FOREIGN KEY that gives the error.

Reproduction: (in any new database)
First create the tables:

CREATE TABLE users (id INT PRIMARY KEY);
CREATE TABLE emails (id INT PRIMARY KEY);

Then run

ALTER TABLE emails ADD FOREIGN KEY (users_id) REFERENCES users(id);

which fails and gives the error SQL string could not be parsed: near FOREIGN, "None": syntax error at (1, 31)

Start by reproducing the SQL statements in a new database and compare the failure with linked issue 447. Trace how ALTER TABLE parses the FOREIGN KEY clause and verify that the completed change accepts the statement and creates the intended reference from emails(users_id) to users(id).