If Any field value of @EmbeddedId is null, which problem will arise?

I have a problem with Hibernate @EmbeddedId.

@Embeddable
public class EnrolRegEmbededId implements Serializable
{
 @Column(name="ENROL_NO")
private String enrolNo;
@Column(name="REG_NO")
private String regNo;
}

@Entity
@Table(name = "PTAX_ENROL_REG_PRINCIPAL_INFO")
public class Enrol_reg_principal_info implements Serializable {

@EmbeddedId
private EnrolRegEmbededId enrolReg;
@Column(name = "APPLN_TYPE")
private String type;
@Column(name = "FIRST_NM")
private String f_name;
@Column(name = "MIDDLE_NM")
private String m_name;
@Column(name = "LAST_NM")
}

I get data from class Enrol_reg_principal_info when both enrolNo and regNo have a value.

Why do I get NUllPointerException when either enrolNo or regNo have no value?

String hql = " from Enrol_reg_principal_info prin where prin.enrolReg.regNo=:id";

to get a value for regNo;

String hql = " from Enrol_reg_principal_info prin where prin.enrolReg.enrolNo=:ec";

to get a value for enrolNO.

public EnrolRegPrinModel masterDetailsEC(String EC) throws Exception {
EnrolRegPrinModel ecDetails = new EnrolRegPrinModel();
Enrol_reg_principal_info info = new Enrol_reg_principal_info();
  
Session s = null;
try {
 s = sessionFactory.openSession();
String hql = " from Enrol_reg_principal_info prin where 
prin.enrolReg.enrolNo=:ec";
  Query q = s.createQuery(hql);
  q.setString("ec", EC);
info = (Enrol_reg_principal_info) q.uniqueResult();
} catch (Exception ex) {
 ex.printStackTrace();
} finally {
 s.close();

 }
 return ecDetails;
}

When you say EmbeddedId, it represents a composite primary key, which expects a non-null and unique value. JPA expects these columns to be non-null and unique. Choose your columns in accordance to that.

Hibernate reference: http://docs.jboss.org/hibernate/orm/5.3/userguide/html_single/Hibernate_User_Guide.html#identifiers-composite-aggregated

Also, I'm not sure if you already have getters and setters. The embedded id class needs to have equals() and hashcode() methods properly set.