fix auto filters for nullable columns

packages/table-core/src/features/column-filtering/columnFilteringFeature.utils.ts

@@ -47,9 +47,18 @@ export function column_getAutoFilterFn<
   const filterFns: Record<string, FilterFn<TFeatures, TData>> | undefined =
     column.table._rowModelFns.filterFns
 
-  const firstRow = column.table.getCoreRowModel().flatRows[0]
+  const rows = column.table.getCoreRowModel().flatRows
+  let value: unknown
 
-  const value = firstRow ? firstRow.getValue(column.id) : undefined
+  // Nullable columns should be inferred from their first available value,
+  // rather than changing filter behavior based on which row happens to lead.
+  for (let i = 0; i < rows.length; i++) {
+    const rowValue = rows[i]!.getValue(column.id)
+    if (rowValue !== null && rowValue !== undefined) {
+      value = rowValue
+      break
+    }
+  }
 
   let filterFnName: string
 

packages/table-core/tests/implementation/features/column-filtering/createFilteredRowModel.test.ts

@@ -511,6 +511,22 @@ describe('createFilteredRowModel', () => {
     })
   })
 
+  it('should auto-filter a nullable string column when the first value is null', () => {
+    type NullableTestRow = { name: string | null }
+    const table = constructTable<typeof features, NullableTestRow>({
+      features,
+      columns: [{ accessorKey: 'name', id: 'name' }],
+      data: [{ name: null }, { name: 'hello' }, { name: 'welcome' }],
+      initialState: {
+        columnFilters: [{ id: 'name', value: 'ell' }],
+      },
+    })
+
+    expect(
+      table.getFilteredRowModel().rows.map((row) => row.original.name),
+    ).toEqual(['hello'])
+  })
+
   describe('unresolvable global filter fn', () => {
     afterEach(() => {
       vi.unstubAllEnvs()

packages/table-core/tests/unit/features/column-filtering/columnFilteringFeature.utils.test.ts

@@ -4,6 +4,7 @@ import {
   constructTable,
   filterFn_arrIncludes,
   filterFn_equals,
+  filterFn_includesString,
   filterFns,
 } from '../../../../src'
 import {
@@ -64,6 +65,19 @@ describe('column_getAutoFilterFn', () => {
 
     expect(column_getAutoFilterFn(column)).toBe(filterFn_equals)
   })
+
+  it('infers the filter from the first non-null column value', () => {
+    type NullableSample = { name: string | null }
+    const table = constructTable({
+      features,
+      columns: [{ accessorKey: 'name', id: 'name' }],
+      data: [{ name: null }, { name: 'hello' }] satisfies Array<NullableSample>,
+    })
+
+    expect(column_getAutoFilterFn(table.getColumn('name')!)).toBe(
+      filterFn_includesString,
+    )
+  })
 })
 
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