Error while creating Order management extension when using getItemclass method

I am getting below error when adding getitemclass view object to my code.

The Warning message when warehouse is empty extension during the On Save event couldn't be completed. oracle.jbo.JboException: JBO-29000: Unexpected exception caught: org.codehaus.groovy.runtime.InvokerInvocationException, msg=groovy.lang.MissingMethodException: No signature of method: ExID300000174083330__81.getItemClass() is applicable for argument types: (Long, Long) values: [100000006481951, 300000002525092] Possible solutions: getMetaClass(), getMetaClass(), getMetaClass(), getClass() RootCause Exception message : groovy.lang.MissingMethodException: No signature of method: ExID300000174083330__81