title: prisma: Why can't I set "null" as default value for nullable columns?
body: <pre><code>model Comment {
    id        Int        @id @default(autoincrement())
    reply     Comment?   @relation(fields: [replyId], references: [id], onDelete: SetNull)
    replyId   Int?       @default(null)
    comment   String
  }
  </code></pre>
  <p>Here both <code>reply</code> and <code>replyId</code> are nullable, but when I try to migrate I get this error:</p>
  <pre><code>error: Error parsing attribute &quot;@default&quot;: Expected a numeric value, but received literal value &quot;Null&quot;.
    --&gt;  schema.prisma:70
     |
  69 |   reply     Comment? @relation(fields: [replyId], references: [id], onDelete: SetNull)
  70 |   replyId   Int?     @default(null)
     |
  </code></pre>
  <p>Can anyone explain the problem?</p>