Default user fields to empty rather than NULL

postgres/1_initial.up.sql

@@ -2,10 +2,10 @@
 CREATE TABLE IF NOT EXISTS "user" (
 	id BYTEA PRIMARY KEY,
 	username VARCHAR(63555) UNIQUE,
-	bio VARCHAR(63535),
-	profile_pic VARCHAR(63535),
-	first_name VARCHAR(65535),
-	last_name VARCHAR(65535),
+	bio VARCHAR(63535) DEFAULT '',
+	profile_pic VARCHAR(63535) DEFAULT '',
+	first_name VARCHAR(65535) DEFAULT '',
+	last_name VARCHAR(65535) DEFAULT '',
 	phone_number VARCHAR(32) UNIQUE
 );