Message Title

"BIT is an integer type that can store the values 0 or 1.
By default, the BIT data type does not allow NULL.
A BIT value requires 1 byte of storage."

CREATE TABLE "dbm"."mytable" (
"id" BIGINT NOT NULL,
"bitfield" BIT,
"tinyintfield" TINYINT,
PRIMARY KEY ( "id" ASC )
) IN "system";

CREATE TABLE "dbm"."mytable" (
"id" BIGINT NOT NULL,
"bitfield" BIT NULL,
"tinyintfield" TINYINT NULL,
PRIMARY KEY ( "id" ASC )
) IN "system";

This is the meaning of "By default, the BIT data type does not allow NULL", if I omit NULL directive on field declaration, by default it is NOT NULL

// Generated Nov 7, 2018 5:29:53 PM by Hibernate Tools 5.2.10.Final

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * Mytable generated by hbm2java
 */
@Entity
@Table(name = "mytable", schema = "dbm")
public class Mytable implements java.io.Serializable {

	private long id;
	private Boolean bitfield; 
	private Byte tinyintfield; 

	public Mytable() {
	}

	public Mytable(long id) {
		this.id = id;
	}

	public Mytable(long id, Boolean bitfield, Byte tinyintfield) {
		this.id = id;
		this.bitfield = bitfield;
		this.tinyintfield = tinyintfield;
	}

	@Id

	@Column(name = "id", nullable = false)
	public long getId() {
		return this.id;
	}

	public void setId(long id) {
		this.id = id;
	}

	@Column(name = "bitfield")
	public Boolean getBitfield() {
		return this.bitfield;
	}

	public void setBitfield(Boolean bitfield) {
		this.bitfield = bitfield;
	}

	@Column(name = "tinyintfield")
	public Byte getTinyintfield() {
		return this.tinyintfield;
	}

	public void setTinyintfield(Byte tinyintfield) {
		this.tinyintfield = tinyintfield;
	}

}

inserting record with null value for Boolean field in my old version of hibernate (5.0.12) in the code:

public SqlTypeDescriptor remapSqlTypeDescriptor(SqlTypeDescriptor sqlTypeDescriptor) {
		if ( sqlTypeDescriptor == null ) {
			throw new IllegalArgumentException( "sqlTypeDescriptor is null" );
		}
		if ( ! sqlTypeDescriptor.canBeRemapped() ) {
			return sqlTypeDescriptor;
		}

		final SqlTypeDescriptor overridden = getSqlTypeDescriptorOverride( sqlTypeDescriptor.getSqlType() );
		return overridden == null ? sqlTypeDescriptor : overridden;
}