Merge pull request #30878 from terminux

* gh-30878:
  Polish "Assert that sources does not contain null elements"
  Assert that sources does not contain null elements

Closes gh-30878

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/Binder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -72,7 +72,7 @@ public class Binder {
 	 * @param sources the sources used for binding
 	 */
 	public Binder(ConfigurationPropertySource... sources) {
-		this(Arrays.asList(sources), null, null, null);
+		this((sources != null) ? Arrays.asList(sources) : null, null, null, null);
 	}
 
 	/**
@@ -182,6 +182,9 @@ public class Binder {
 			List<ConversionService> conversionServices, Consumer<PropertyEditorRegistry> propertyEditorInitializer,
 			BindHandler defaultBindHandler, BindConstructorProvider constructorProvider) {
 		Assert.notNull(sources, "Sources must not be null");
+		for (ConfigurationPropertySource source : sources) {
+			Assert.notNull(source, "Sources must not contain null elements");
+		}
 		this.sources = sources;
 		this.placeholdersResolver = (placeholdersResolver != null) ? placeholdersResolver : PlaceholdersResolver.NONE;
 		this.bindConverter = BindConverter.get(conversionServices, propertyEditorInitializer);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/BinderTests.java

@@ -70,11 +70,29 @@ class BinderTests {
 	private Binder binder = new Binder(this.sources);
 
 	@Test
-	void createWhenSourcesIsNullShouldThrowException() {
+	void createWhenSourcesIsNullArrayShouldThrowException() {
+		assertThatIllegalArgumentException().isThrownBy(() -> new Binder((ConfigurationPropertySource[]) null))
+				.withMessageContaining("Sources must not be null");
+	}
+
+	@Test
+	void creatWhenSourcesIsNullIterableShouldThrowException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new Binder((Iterable<ConfigurationPropertySource>) null))
 				.withMessageContaining("Sources must not be null");
 	}
 
+	@Test
+	void createWhenArraySourcesContainsNullElementShouldThrowException() {
+		assertThatIllegalArgumentException().isThrownBy(() -> new Binder(new ConfigurationPropertySource[] { null }))
+				.withMessageContaining("Sources must not contain null elements");
+	}
+
+	@Test
+	void createWhenIterableSourcesContainsNullElementShouldThrowException() {
+		assertThatIllegalArgumentException().isThrownBy(() -> new Binder(Collections.singletonList(null)))
+				.withMessageContaining("Sources must not contain null elements");
+	}
+
 	@Test
 	void bindWhenNameIsNullShouldThrowException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> this.binder.bind((ConfigurationPropertyName) null,