Remove Order in hibernate

The problem seems to be that the column IDCONTRACTin the table that holds Timesheets has a NOT NULL restriction. Remove it and try again.

If you're autogenerating the schema, try adding @Basic(optional = true) to Timesheet.companyContract:

@Basic(optional = true)
@ManyToOne
@JoinColumn(name = "IDCONTRACT")
private CompanyContract companyContract;