Environment:
 - Windows 2000 Server
 - Apache v1.3.20 (binaries from www.apache.org)
 - PHP v4.0.6 (binaries from www.php.net)
 - InterBase v6.0.0.627 (binaries from www.borland.com)

1. Let's create very simple database:
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CREATE DATABASE 'c:\db\test.gdb'
USER 'user' PASSWORD 'password';

CREATE TABLE TEST_TABLE (
    INT_VALUE INTEGER,
    STR_VALUE VARCHAR(50));

COMMIT WORK;
-----------------------------------------------------------------

2. Create very simple PHP script:
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<?php
$ib = ibase_connect('c:\db\test.gdb','user','password');

$query = ibase_prepare($ib,'insert into TEST_TABLE_2(INT_VALUE, STR_VALUE) values (?, ?)');
$rs = ibase_execute($query,1,null);

ibase_close($ib);
?>
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After this script will be executed, TEST_TABLE table will contain a row with STR_VALUE='' instead of NULL!

 However inserting the same data through ibase_query() works properly.