Protect against null names when filter is applied more than once

Update `FilteredIterableConfigurationPropertiesSource` to fix a
regression caused by commit 8f14dca1 that occurs if the `filter()`
method is called on an already filtered source.

Fixes gh-46032

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/FilteredIterableConfigurationPropertiesSource.java

@@ -41,6 +41,9 @@ class FilteredIterableConfigurationPropertiesSource extends FilteredConfiguratio
 			this.filteredNames = new ConfigurationPropertyName[filterableNames.length];
 			this.numerOfFilteredNames = 0;
 			for (ConfigurationPropertyName name : filterableNames) {
+				if (name == null) {
+					break;
+				}
 				if (filter.test(name)) {
 					this.filteredNames[this.numerOfFilteredNames++] = name;
 				}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/FilteredIterableConfigurationPropertiesSourceTests.java

@@ -74,6 +74,24 @@ class FilteredIterableConfigurationPropertiesSourceTests extends FilteredConfigu
 			.containsExactly("a", "b", "c");
 	}
 
+	@Test
+	void iteratorWhenSpringPropertySourceAndAnotherFilterFiltersNames() {
+		IterableConfigurationPropertySource testSource = (IterableConfigurationPropertySource) createTestSource();
+		Map<String, Object> map = new LinkedHashMap<>();
+		for (ConfigurationPropertyName name : testSource) {
+			map.put(name.toString(), testSource.getConfigurationProperty(name).getValue());
+		}
+		PropertySource<?> propertySource = new OriginTrackedMapPropertySource("test", map, true);
+		SpringConfigurationPropertySource source = SpringConfigurationPropertySource.from(propertySource);
+		IterableConfigurationPropertySource filtered = (IterableConfigurationPropertySource) source
+			.filter(this::noBrackets);
+		IterableConfigurationPropertySource secondFiltered = filtered.filter((name) -> !name.toString().contains("c"));
+		assertThat(Extractors.byName("filteredNames").apply(filtered)).isNotNull();
+		assertThat(secondFiltered.iterator()).toIterable()
+			.extracting(ConfigurationPropertyName::toString)
+			.containsExactly("a", "b");
+	}
+
 	@Test
 	void containsDescendantOfWhenSpringPropertySourceUsesContents() {
 		Map<String, Object> map = new LinkedHashMap<>();