Oracle 12g XmlType store as Binary XML (select issue)

Question

I am trying to select XML from DB Oracle12g. XML is stored in the table (XMLType store as binary XML) and I am not able to create Select query with where-condition. My problem is that query doesn't return any record. I am using Oracle SQL Developer 4.1.0.19.

Examples of my queries

SELECT OBJECT_VALUE
  FROM A_STUDENT_BIN
 WHERE existsNode(object_value,'//Student[@RodneCislo="123"]') = 1;

SELECT OBJECT_VALUE
  FROM A_STUDENT_BIN
 WHERE extract(OBJECT_VALUE, '//Student[@RodneCislo="123"]') IS NOT NULL;

Table Structure:

CREATE TABLE a_student_bin OF XMLTYPE XMLTYPE STORE AS BINARY XML;

Inserted XML

<?xml version="1.0" encoding="windows-1250" ?>
<Vystup>
  <Student RodneCislo="123">
    <Jmeno>Pepa</Jmeno>
    <Prijmeni>Omacka</Prijmeni>
    <TitulPred>Ing.</TitulPred>
    <TitulZa></TitulZa>
  </Student>
</Vystup>

XML was inserted into db by query:

insert into A_STUDENT_BIN
values (XmlType( bfilename('MYDIR','student.xml'),
                 nls_charset_id('EE8MSWIN1250')   );