Hi tmmaluleke!
You got a typing error in your exclusive gateway. You wrote "student" instead of "studentId" ;-)
<sequenceFlow id="_5-_6" sourceRef="_5" targetRef="_6" name="Accept" tns:priority="1" >
<conditionExpression xsi:type="tFormalExpression" language="http://www.java.com/java" >return student =true;</conditionExpression>
</sequenceFlow>
<sequenceFlow id="_5-_7" sourceRef="_5" targetRef="_7" name="Reject" tns:priority="1" >
<conditionExpression xsi:type="tFormalExpression" language="http://www.java.com/java" >return studentId=false;</conditionExpression>
</sequenceFlow>