Enforce non-null contract on vector elements.

Also add shortcuts for empty sources and simplify copy calls that do not transform source values.

See #3193
Original pull request: #3194

src/main/java/org/springframework/data/domain/DoubleVector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 the original author or authors.
+ * Copyright 2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,7 +30,7 @@ class DoubleVector implements Vector {
 
 	private final double[] v;
 
-	public DoubleVector(double[] v) {
+	DoubleVector(double[] v) {
 		this.v = v;
 	}
 
@@ -39,10 +39,11 @@ class DoubleVector implements Vector {
 	 */
 	static Vector copy(double[] v) {
 
-		double[] copy = new double[v.length];
-		System.arraycopy(v, 0, copy, 0, copy.length);
+		if (v.length == 0) {
+			return new DoubleVector(new double[0]);
+		}
 
-		return new DoubleVector(copy);
+		return new DoubleVector(Arrays.copyOf(v, v.length));
 	}
 
 	/**
@@ -50,6 +51,10 @@ class DoubleVector implements Vector {
 	 */
 	static Vector copy(Collection<? extends Number> v) {
 
+		if (v.isEmpty()) {
+			return new DoubleVector(new double[0]);
+		}
+
 		double[] copy = new double[v.size()];
 		int i = 0;
 		for (Number number : v) {
@@ -87,11 +92,7 @@ class DoubleVector implements Vector {
 
 	@Override
 	public double[] toDoubleArray() {
-
-		double[] copy = new double[this.v.length];
-		System.arraycopy(this.v, 0, copy, 0, copy.length);
-
-		return copy;
+		return Arrays.copyOf(this.v, this.v.length);
 	}
 
 	@Override

src/main/java/org/springframework/data/domain/FloatVector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 the original author or authors.
+ * Copyright 2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,7 +30,7 @@ class FloatVector implements Vector {
 
 	private final float[] v;
 
-	public FloatVector(float[] v) {
+	FloatVector(float[] v) {
 		this.v = v;
 	}
 
@@ -39,10 +39,11 @@ class FloatVector implements Vector {
 	 */
 	static Vector copy(float[] v) {
 
-		float[] copy = new float[v.length];
-		System.arraycopy(v, 0, copy, 0, copy.length);
+		if (v.length == 0) {
+			return new FloatVector(new float[0]);
+		}
 
-		return new FloatVector(copy);
+		return new FloatVector(Arrays.copyOf(v, v.length));
 	}
 
 	/**
@@ -50,6 +51,10 @@ class FloatVector implements Vector {
 	 */
 	static Vector copy(Collection<? extends Number> v) {
 
+		if (v.isEmpty()) {
+			return new FloatVector(new float[0]);
+		}
+
 		float[] copy = new float[v.size()];
 		int i = 0;
 		for (Number number : v) {
@@ -76,11 +81,7 @@ class FloatVector implements Vector {
 
 	@Override
 	public float[] toFloatArray() {
-
-		float[] copy = new float[this.v.length];
-		System.arraycopy(this.v, 0, copy, 0, copy.length);
-
-		return copy;
+		return Arrays.copyOf(this.v, this.v.length);
 	}
 
 	@Override

src/main/java/org/springframework/data/domain/NumberVector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 the original author or authors.
+ * Copyright 2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.data.domain;
 import java.util.Arrays;
 import java.util.Collection;
 
+import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -30,7 +31,9 @@ class NumberVector implements Vector {
 
 	private final Number[] v;
 
-	public NumberVector(Number[] v) {
+	NumberVector(Number[] v) {
+
+		Assert.noNullElements(v, "Vector [v] must not contain null elements");
 		this.v = v;
 	}
 
@@ -39,41 +42,39 @@ class NumberVector implements Vector {
 	 */
 	static Vector copy(Number[] v) {
 
-		Number[] copy = new Number[v.length];
-		System.arraycopy(v, 0, copy, 0, copy.length);
+		if (v.length == 0) {
+			return new NumberVector(new Number[0]);
+		}
 
-		return new NumberVector(copy);
+		return new NumberVector(Arrays.copyOf(v, v.length));
 	}
 
 	/**
 	 * Copy the given {@link Number} and wrap it within a Vector.
 	 */
-	static Vector copy(Collection<? extends Number> numbers) {
+	static Vector copy(Collection<? extends Number> v) {
 
-		Number[] copy = new Number[numbers.size()];
-
-		int i = 0;
-		for (Number number : numbers) {
-			copy[i++] = number;
+		if (v.isEmpty()) {
+			return new NumberVector(new Number[0]);
 		}
 
-		return new NumberVector(copy);
+		return new NumberVector(v.toArray(Number[]::new));
 	}
 
 	@Override
 	public Class<? extends Number> getType() {
 
-		Class<?> candidate = null;
-		for (Object val : v) {
-			if (val != null) {
-				if (candidate == null) {
-					candidate = val.getClass();
-				} else if (candidate != val.getClass()) {
-					return Number.class;
-				}
+		if (this.v.length == 0) {
+			return Number.class;
+		}
+
+		Class<? extends Number> candidate = this.v[0].getClass();
+		for (int i = 1; i < this.v.length; i++) {
+			if (candidate != this.v[i].getClass()) {
+				return Number.class;
 			}
 		}
-		return (Class<? extends Number>) candidate;
+		return candidate;
 	}
 
 	@Override

src/main/java/org/springframework/data/domain/Vector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 the original author or authors.
+ * Copyright 2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -75,6 +75,9 @@ public interface Vector {
 	static Vector of(Collection<? extends Number> values) {
 
 		Assert.notNull(values, "Vector values must not be null");
+		if(values.isEmpty()) {
+			return NumberVector.copy(new Number[0]);
+		}
 
 		Class<?> cet = CollectionUtils.findCommonElementType(values);
 

src/test/java/org/springframework/data/domain/FloatVectorUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 the original author or authors.
+ * Copyright 2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

src/test/java/org/springframework/data/domain/NumberVectorUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 the original author or authors.
+ * Copyright 2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,9 +15,12 @@
  */
 package org.springframework.data.domain;
 
-import static org.assertj.core.api.Assertions.*;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
 
 import org.junit.jupiter.api.Test;
 
@@ -25,12 +28,40 @@ import org.junit.jupiter.api.Test;
  * Unit tests for {@link NumberVector}.
  *
  * @author Mark Paluch
+ * @author Christoph Strobl
  */
 class NumberVectorUnitTests {
 
 	Number[] values = new Number[] { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6f };
 	Number[] floats = new Number[] { (float) 1.1d, (float) 2.2d, (float) 3.3d, (float) 4.4d, (float) 5.5, 6.6 };
 
+	@Test // GH-3193
+	void shouldErrorOnNullElements() {
+
+		List<Long> source = new ArrayList<>(3);
+		source.add(1L);
+		source.add(null);
+		source.add(3L);
+
+		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> NumberVector.copy(source));
+		assertThatExceptionOfType(IllegalArgumentException.class)
+				.isThrownBy(() -> NumberVector.copy(new Number[] { 1L, null, 3L }));
+	}
+
+	@Test // GH-3193
+	void shouldAcceptEmptySource() {
+
+		Vector vector = NumberVector.copy(List.of());
+
+		assertThat(vector.size()).isEqualTo(0);
+		assertThat(vector.getType()).isEqualTo(Number.class);
+
+		vector = NumberVector.copy(new Number[] {});
+
+		assertThat(vector.size()).isEqualTo(0);
+		assertThat(vector.getType()).isEqualTo(Number.class);
+	}
+
 	@Test // GH-3193
 	void shouldCreateVector() {
 
@@ -48,6 +79,17 @@ class NumberVectorUnitTests {
 		assertThat(vector.getSource()).isNotSameAs(vector).isEqualTo(values);
 	}
 
+	@Test // GH-3193
+	void shouldFigureOutCommonType() {
+
+		assertThat(NumberVector.copy(List.of()).getType()).isEqualTo(Number.class);
+		assertThat(NumberVector.copy(List.of(1)).getType()).isEqualTo(Integer.class);
+		assertThat(NumberVector.copy(List.of(1L, 2L)).getType()).isEqualTo(Long.class);
+		assertThat(NumberVector.copy(List.of(1F, 2F)).getType()).isEqualTo(Float.class);
+		assertThat(NumberVector.copy(List.of(1D, 2D)).getType()).isEqualTo(Double.class);
+		assertThat(NumberVector.copy(List.of(1D, 2F, 3F)).getType()).isEqualTo(Number.class);
+	}
+
 	@Test // GH-3193
 	void shouldRenderToString() {
 
@@ -66,7 +108,7 @@ class NumberVectorUnitTests {
 	}
 
 	@Test // GH-3193
-	void sourceShouldReturnSource() {
+	void sourceShouldReturnSource() { // this one is questionable
 
 		Vector vector = new NumberVector(values);
 

src/test/java/org/springframework/data/domain/VectorUnitTests.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.domain;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+import java.util.Collection;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Christoph Strobl
+ */
+public class VectorUnitTests {
+
+	@Test // GH-3193
+	void staticInitializersErrorOnNull() {
+
+		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> Vector.of((double[]) null));
+		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> Vector.of((float[]) null));
+		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> Vector.of((Collection<Number>) null));
+	}
+}