Declare contacts - Add form data.. - Error

I'm new on Bonitasoft.
I try to create project following Bonitasoft document.
In declare contact section : Declare contracts | Bonita Documentation (bonitasoft.com)
I can't Add fom data, When I click finish it's will show error :

An error occurred while generating the contract from a data.
org.bonitasoft.studio.groovy.GroovyCompilationUnitFactory.newCompilationUnit(GroovyCompilationUnitFactory.java:47)
org.bonitasoft.studio.contract.core.mapping.expression.FieldToContractInputMappingExpressionBuilder.groovyCompilationUnit(FieldToContractInputMappingExpressionBuilder.java:131)
org.bonitasoft.studio.contract.core.mapping.expression.FieldToContractInputMappingExpressionBuilder.addScriptDependencies(FieldToContractInputMappingExpressionBuilder.java:107)
org.bonitasoft.studio.contract.core.mapping.expression.FieldToContractInputMappingExpressionBuilder.toExpression(FieldToContractInputMappingExpressionBuilder.java:73)
org.bonitasoft.studio.contract.core.mapping.operation.FieldToContractInputMappingOperationBuilder.toOperation(FieldToContractInputMappingOperationBuilder.java:59)
org.bonitasoft.studio.contract.core.mapping.RootContractInputGenerator.buildOperations(RootContractInputGenerator.java:99)
org.bonitasoft.studio.contract.core.mapping.RootContractInputGenerator.build(RootContractInputGenerator.java:78)
org.bonitasoft.studio.contract.ui.wizard.ContractInputGenerationWizard.lambda$0(ContractInputGenerationWizard.java:231)
org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:122)

please help

ps. if anyone have tutorial todo CRUD. please provide me.