types/model: fix parser for empty values

types/model/file.go

@@ -249,10 +249,6 @@ func quote(s string) string {
 }
 
 func unquote(s string) (string, bool) {
-	if len(s) == 0 {
-		return "", false
-	}
-
 	// TODO: single quotes
 	if len(s) >= 3 && s[:3] == `"""` {
 		if len(s) >= 6 && s[len(s)-3:] == `"""` {

types/model/file_test.go

@@ -489,6 +489,10 @@ You are a store greeter. Always responsed with "Hello!".
 """
 MESSAGE user Hey there!
 MESSAGE assistant Hello, I want to parse all the things!
+`,
+		`
+FROM foo
+SYSTEM ""
 `,
 	}