Cannot read property 'length' of undefined at NbTreeGridComponent._getAllRenderRows

ERROR TypeError: Cannot read property 'length' of undefined
at NbTreeGridComponent._getAllRenderRows (table.js:1579)
at NbTreeGridComponent.renderRows (table.js:1292)
at NbTreeGridComponent._forceRenderDataRows (table.js:2012)
at NbTreeGridComponent._renderUpdatedColumns (table.js:1694)
at NbTreeGridComponent.ngAfterContentChecked (table.js:1248)
at callProviderLifecycles (core.js:24903)
at callElementProvidersLifecycles (core.js:24872)
at callLifecycleHooksChildrenFirst (core.js:24854)
at checkAndUpdateView (core.js:35060)
at callViewAction (core.js:35421)
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in .ts
customColumn = 'Category';
defaultColumns = ['Formulary', 'Quantity', 'Price', 'Manufacturer',
'Brand', 'Supplier', 'Authority', 'Contract', 'Remarks', 'Year'];
allColumns = [this.customColumn, ...this.defaultColumns];

I followed the example from nebular documentation.

When I use column names till 'Manufacturer' which counts to a total of 5 columns, everything works fine, but when I exceed, it gives the error, I don't have any children data