Description:
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When using oci_bind_by_name to set the value of a field which has a foreign key constraint, the statement fails with a ORA-02291 error (foreign key constraint violation) if the field is of a numeric type and the parameter is given a NULL value.

Reproduce code:
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Steps to reproduce: http://pastie.org/965413

The following patch solves the problem: http://pastie.org/965425

Expected result:
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The field should be given a NULL value without violating the foreign key constraint.

Actual result:
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The statement fails with a ORA-02291 error (integrity constraint ([constraint name]) violated - parent key not found).