diff --git a/packages/bindx/src/dataview/filterHandlers.ts b/packages/bindx/src/dataview/filterHandlers.ts
index e0ab103..1448b0e 100644
--- a/packages/bindx/src/dataview/filterHandlers.ts
+++ b/packages/bindx/src/dataview/filterHandlers.ts
@@ -393,16 +393,16 @@ export function createRelationFilterHandler(fieldPath: string): FilterHandler<Re
 export function createIsDefinedFilterHandler(fieldPath: string): FilterHandler<IsDefinedFilterArtifact> {
 	return {
 		defaultArtifact(): IsDefinedFilterArtifact {
-			return { defined: null }
+			return {}
 		},
 
 		isActive(artifact: IsDefinedFilterArtifact): boolean {
-			return artifact.defined !== null
+			return artifact.nullCondition !== undefined
 		},
 
 		toWhere(artifact: IsDefinedFilterArtifact): Record<string, unknown> | undefined {
-			if (artifact.defined === null) return undefined
-			return buildNestedWhere(fieldPath, { isNull: !artifact.defined })
+			if (artifact.nullCondition === undefined) return undefined
+			return buildNestedWhere(fieldPath, { isNull: artifact.nullCondition })
 		},
 	}
 }
diff --git a/packages/bindx/src/dataview/types.ts b/packages/bindx/src/dataview/types.ts
index 81face1..7eacc42 100644
--- a/packages/bindx/src/dataview/types.ts
+++ b/packages/bindx/src/dataview/types.ts
@@ -88,7 +88,12 @@ export interface EnumListFilterArtifact {
  * IsDefined filter artifact
  */
 export interface IsDefinedFilterArtifact {
-	readonly defined: boolean | null
+	/**
+	 * Follows the shared `nullCondition` convention used by every other filter handler.
+	 * `false` = exclude nulls (is-defined); `true` = include-nulls-only (not-defined);
+	 * `undefined` = filter inactive.
+	 */
+	readonly nullCondition?: boolean
 }
 
 /**
diff --git a/tests/unit/dataview/filterHandlers.test.ts b/tests/unit/dataview/filterHandlers.test.ts
index 99b146a..37c70ef 100644
--- a/tests/unit/dataview/filterHandlers.test.ts
+++ b/tests/unit/dataview/filterHandlers.test.ts
@@ -274,19 +274,19 @@ describe('filter handlers', () => {
 	describe('isDefined filter', () => {
 		const handler = createIsDefinedFilterHandler('publishedAt')
 
-		test('defined = true → isNull: false', () => {
-			const where = handler.toWhere({ defined: true })
+		test('nullCondition = false (is-defined) → isNull: false', () => {
+			const where = handler.toWhere({ nullCondition: false })
 			expect(where).toEqual({ publishedAt: { isNull: false } })
 		})
 
-		test('defined = false → isNull: true', () => {
-			const where = handler.toWhere({ defined: false })
+		test('nullCondition = true (not-defined) → isNull: true', () => {
+			const where = handler.toWhere({ nullCondition: true })
 			expect(where).toEqual({ publishedAt: { isNull: true } })
 		})
 
-		test('defined = null is inactive', () => {
-			expect(handler.isActive({ defined: null })).toBe(false)
-			expect(handler.toWhere({ defined: null })).toBeUndefined()
+		test('nullCondition undefined is inactive', () => {
+			expect(handler.isActive({})).toBe(false)
+			expect(handler.toWhere({})).toBeUndefined()
 		})
 	})
 
@@ -299,7 +299,7 @@ describe('filter handlers', () => {
 
 		test('isDefined filter on nested path', () => {
 			const handler = createIsDefinedFilterHandler('author.email')
-			const where = handler.toWhere({ defined: true })
+			const where = handler.toWhere({ nullCondition: false })
 			expect(where).toEqual({ author: { email: { isNull: false } } })
 		})
 	})
diff --git a/tests/unit/dataview/isDefinedHandlerNullConditionCompat.test.ts b/tests/unit/dataview/isDefinedHandlerNullConditionCompat.test.ts
new file mode 100644
index 0000000..c4a075f
--- /dev/null
+++ b/tests/unit/dataview/isDefinedHandlerNullConditionCompat.test.ts
@@ -0,0 +1,54 @@
+// Regression test for <issue-url — filled in after Step 7>
+//
+// `DataGridIsDefinedFilterControls` (bindx-ui) drives `DataViewNullFilterTrigger`,
+// which writes a `nullCondition: boolean` field onto the filter artifact via
+// `useDataViewNullFilter`. That field is the convention used by every other
+// filter handler (text/number/date/enum/relation/boolean) — see e.g.
+// `filterHandlers.test.ts > text filter > with null condition`.
+//
+// `createIsDefinedFilterHandler` is the outlier: its `IsDefinedFilterArtifact`
+// shape is `{ defined: boolean | null }`. The handler's `isActive` and `toWhere`
+// only inspect `defined` — `nullCondition` is completely ignored. So when the
+// bindx-ui filter UI writes `nullCondition`, the handler never wakes up and
+// the filter has no effect.
+//
+// `DataGridIsDefinedColumn` (in bindx-ui) wires these two together, but the
+// combination is non-functional today and there are no existing usages to
+// have caught it.
+import '../../setup'
+import { describe, expect, test } from 'bun:test'
+import { createIsDefinedFilterHandler } from '@contember/bindx'
+
+describe('createIsDefinedFilterHandler integration with DataViewNullFilterTrigger', () => {
+	const handler = createIsDefinedFilterHandler('email')
+
+	test('should treat artifact as active when DataGridIsDefinedFilterControls writes nullCondition: false (✓ button)', () => {
+		// `DataGridIsDefinedFilterControls`'s ✓ button uses
+		// `DataViewNullFilterTrigger action="toggleExclude"`, which calls
+		// `useDataViewNullFilter`'s `toggleExclude` branch:
+		//
+		//   setFilter(it => ({ ...it, nullCondition: it?.nullCondition === false ? undefined : false }))
+		//
+		// Starting from the default artifact, this writes `nullCondition: false`.
+		const afterExcludeClick = {
+			...handler.defaultArtifact(),
+			nullCondition: false,
+		} as never
+
+		expect(handler.isActive(afterExcludeClick)).toBe(true)
+		expect(handler.toWhere(afterExcludeClick)).toEqual({ email: { isNull: false } })
+	})
+
+	test('should treat artifact as active when DataGridIsDefinedFilterControls writes nullCondition: true (✗ button)', () => {
+		// `DataGridIsDefinedFilterControls`'s ✗ button uses
+		// `DataViewNullFilterTrigger action="toggleInclude"`, which sets
+		// `nullCondition: true`.
+		const afterIncludeClick = {
+			...handler.defaultArtifact(),
+			nullCondition: true,
+		} as never
+
+		expect(handler.isActive(afterIncludeClick)).toBe(true)
+		expect(handler.toWhere(afterIncludeClick)).toEqual({ email: { isNull: true } })
+	})
+})