Correct handling of beans with null definitions when finding matches

Fixes gh-48117

Author: wilkinsona

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/OnBeanCondition.java

@@ -471,11 +471,19 @@ private Map<String, BeanDefinition> getBeanDefinitions(ConfigurableListableBeanF
 	}
 
 	private List<String> getPrimaryBeans(Map<String, BeanDefinition> beanDefinitions) {
-		return getMatchingBeans(beanDefinitions, BeanDefinition::isPrimary);
+		return getMatchingBeans(beanDefinitions, this::isPrimary);
+	}
+
+	private boolean isPrimary(BeanDefinition beanDefinition) {
+		return (beanDefinition != null) && beanDefinition.isPrimary();
 	}
 
 	private List<String> getNonFallbackBeans(Map<String, BeanDefinition> beanDefinitions) {
-		return getMatchingBeans(beanDefinitions, Predicate.not(BeanDefinition::isFallback));
+		return getMatchingBeans(beanDefinitions, this::isNotFallback);
+	}
+
+	private boolean isNotFallback(BeanDefinition beanDefinition) {
+		return (beanDefinition == null) || !beanDefinition.isFallback();
 	}
 
 	private List<String> getMatchingBeans(Map<String, BeanDefinition> beanDefinitions, Predicate<BeanDefinition> test) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnSingleCandidateTests.java

@@ -195,6 +195,16 @@ void singleCandidateMultipleCandidatesOneDefaultCandidate() {
 			});
 	}
 
+	@Test
+	void singleCandidateDoesNotMatchWhenMultipleRegisteredAsSingletonCandidates() {
+		this.contextRunner.withInitializer((context) -> {
+			context.getBeanFactory().registerSingleton("alpha", "alpha");
+			context.getBeanFactory().registerSingleton("bravo", "bravo");
+		})
+			.withUserConfiguration(OnBeanSingleCandidateConfiguration.class)
+			.run((context) -> assertThat(context).doesNotHaveBean("consumer"));
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnSingleCandidate(String.class)
 	static class OnBeanSingleCandidateConfiguration {