While using Catalyst to insert a book record, error occurs. After searching info from google, no solution is found. Would you pls offer some advice ? Here is the controller's code.

sub url_create : Local {
        # In addition to self & context, get the title, rating, & 
        # author_id args from the URL.  Note that Catalyst automatical
+ly 
        # puts extra information after the "/<controller_name>/<action
+_name/" 
        # into @_
        my ($self, $c, $title, $rating, $author_id) = @_;
    
        # Call create() on the book model object. Pass the table 
        # columns/field values we want to set as hash values
        my $book = $c->model('DB::Books')->create({
                title  => $title,
                rating => $rating
            });
        
        # Add a record to the join table for this book, mapping to 
        # appropriate author
        $book->add_to_book_authors({author_id => $author_id});
        # Note: Above is a shortcut for this:
        # $book->create_related('book_authors', {author_id => $author_
+id});
        
        # Assign the Book object to the stash for display in the view
        $c->stash->{book} = $book;
    
        # This is a hack to disable XSUB processing in Data::Dumper
        # (it's used in the view).  This is a work-around for a bug in
        # the interaction of some versions or Perl, Data::Dumper & DBI
+C.
        # You won't need this if you aren't using Data::Dumper (or if
        # you are running DBIC 0.06001 or greater), but adding it does
+n't 
        # hurt anything either.
        $Data::Dumper::Useperl = 1;
    
        # Set the TT template to use
        $c->stash->{template} = 'books/create_done.tt2';
    }
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However, after accessing URL "http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4", error shows up as :

INSERT INTO books (rating, title) VALUES (?, ?): '5', 'TCPIP_Illustrat
+ed_Vol-2'
SELECT COUNT( * ) FROM books me:
SELECT COUNT( * ) FROM books me:
[info] *** Request 1 (0.038/s) [5225] [Thu Aug 14 15:29:27 2008] ***
[debug] "GET" request for "books/url_create/TCPIP_Illustrated_Vol-2/5/
+4" from "202.38.40.128"
[debug] Path is "books/url_create"
[debug] Arguments are "TCPIP_Illustrated_Vol-2/5/4"
[error] DBI Exception: DBD::Oracle::st execute failed: ORA-01400: cann
+ot insert NULL into ("SDB2"."BOOKS"."ID") (DBD ERROR: OCIStmtExecute)
+ [for Statement "INSERT INTO books (rating, title) VALUES (?, ?)" wit
+h ParamValues: :p1='5', :p2='TCPIP_Illustrated_Vol-2'] at /usr/local/
+lib/perl5/site_perl/5.10.0/DBIx/Class/Schema.pm line 954
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