Steps to Reproduce

1. run the attached zul with the 5.8.0 latest FL
2. click the button to clone a sheet

Current Result

java.lang.NullPointerException
at org.zkoss.poi.ss.formula.FormulaCellCache.get(FormulaCellCache.java:56)
at org.zkoss.poi.ss.formula.EvaluationCache.notifyClearIterationValue(EvaluationCache.java:228)
at org.zkoss.poi.ss.formula.WorkbookEvaluator.notifyClearIterationValue(WorkbookEvaluator.java:246)
at io.keikai.model.impl.sys.formula.FormulaEngineImpl.clearIterationValue(FormulaEngineImpl.java:767)
at io.keikai.model.impl.CellImpl.setValue(CellImpl.java:489)
at io.keikai.model.impl.CellImpl.setValue(CellImpl.java:426)
at io.keikai.model.impl.CellImpl.setFormulaValue(CellImpl.java:285)
at io.keikai.model.impl.CellImpl.setFormulaValue(CellImpl.java:259)
at io.keikai.model.impl.CellImpl.setValue(CellImpl.java:445)
at io.keikai.model.impl.CellImpl.setValue(CellImpl.java:426)
at io.keikai.model.impl.CellImpl.cloneCell(CellImpl.java:697)
at io.keikai.model.impl.RowImpl.cloneRow(RowImpl.java:321)
at io.keikai.model.impl.SheetImpl.copyToBook(SheetImpl.java:951)
at io.keikai.model.impl.SheetImpl.copyTo(SheetImpl.java:906)
at io.keikai.model.impl.BookImpl.createSheet(BookImpl.java:364)
at io.keikai.range.impl.RangeImpl$36.doInvoke(RangeImpl.java:1472)
at io.keikai.range.impl.RangeImpl$ModelManipulationTask.invoke(RangeImpl.java:1865)
at io.keikai.model.util.ReadWriteTask.doInWriteLock(ReadWriteTask.java:43)
at io.keikai.range.impl.RangeImpl.cloneSheet(RangeImpl.java:1484)
at io.keikai.api.impl.RangeImpl.cloneSheet(RangeImpl.java:696)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)

Expected Result

a new sheet with the same content added without errors

Debug Information

• 5.7.0 doesn't have this bug
• related to KEIKAI-453
• io.keikai.issue.IssueK201Test also failed for the same reason