diff --git a/core/spring-boot/src/main/java/org/springframework/boot/DefaultApplicationArguments.java b/core/spring-boot/src/main/java/org/springframework/boot/DefaultApplicationArguments.java
index e2ea20c32ea..190aa8dcab0 100644
--- a/core/spring-boot/src/main/java/org/springframework/boot/DefaultApplicationArguments.java
+++ b/core/spring-boot/src/main/java/org/springframework/boot/DefaultApplicationArguments.java
@@ -16,9 +16,7 @@
 
 package org.springframework.boot;
 
-import java.util.Arrays;
 import java.util.Collections;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -53,7 +51,7 @@ public String[] getSourceArgs() {
 	@Override
 	public Set<String> getOptionNames() {
 		String[] names = this.source.getPropertyNames();
-		return Collections.unmodifiableSet(new HashSet<>(Arrays.asList(names)));
+		return Set.of(names);
 	}
 
 	@Override
diff --git a/core/spring-boot/src/main/java/org/springframework/boot/EnvironmentConverter.java b/core/spring-boot/src/main/java/org/springframework/boot/EnvironmentConverter.java
index dacf5bc9304..880b35da108 100644
--- a/core/spring-boot/src/main/java/org/springframework/boot/EnvironmentConverter.java
+++ b/core/spring-boot/src/main/java/org/springframework/boot/EnvironmentConverter.java
@@ -17,7 +17,6 @@
 package org.springframework.boot;
 
 import java.lang.reflect.Constructor;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -44,11 +43,9 @@ final class EnvironmentConverter {
 	private static final Set<String> SERVLET_ENVIRONMENT_SOURCE_NAMES;
 
 	static {
-		Set<String> names = new HashSet<>();
-		names.add(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME);
-		names.add(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME);
-		names.add(StandardServletEnvironment.JNDI_PROPERTY_SOURCE_NAME);
-		SERVLET_ENVIRONMENT_SOURCE_NAMES = Collections.unmodifiableSet(names);
+		SERVLET_ENVIRONMENT_SOURCE_NAMES = Set.of(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME,
+				StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME,
+				StandardServletEnvironment.JNDI_PROPERTY_SOURCE_NAME);
 	}
 
 	private final ClassLoader classLoader;
diff --git a/core/spring-boot/src/main/java/org/springframework/boot/ExitCodeGenerators.java b/core/spring-boot/src/main/java/org/springframework/boot/ExitCodeGenerators.java
index 9c29dfd8284..b55202266f8 100644
--- a/core/spring-boot/src/main/java/org/springframework/boot/ExitCodeGenerators.java
+++ b/core/spring-boot/src/main/java/org/springframework/boot/ExitCodeGenerators.java
@@ -41,12 +41,6 @@ class ExitCodeGenerators implements Iterable<ExitCodeGenerator> {
 
 	private final List<ExitCodeGenerator> generators = new ArrayList<>();
 
-	void addAll(Throwable exception, ExitCodeExceptionMapper... mappers) {
-		Assert.notNull(exception, "'exception' must not be null");
-		Assert.notNull(mappers, "'mappers' must not be null");
-		addAll(exception, Arrays.asList(mappers));
-	}
-
 	void addAll(Throwable exception, Iterable<? extends ExitCodeExceptionMapper> mappers) {
 		Assert.notNull(exception, "'exception' must not be null");
 		Assert.notNull(mappers, "'mappers' must not be null");
diff --git a/core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListeners.java b/core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListeners.java
index 522fec60684..42aa6de6831 100644
--- a/core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListeners.java
+++ b/core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListeners.java
@@ -28,7 +28,6 @@
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.metrics.ApplicationStartup;
 import org.springframework.core.metrics.StartupStep;
-import org.springframework.util.ReflectionUtils;
 
 /**
  * A collection of {@link SpringApplicationRunListener}.
@@ -99,9 +98,6 @@ private void callFailedListener(SpringApplicationRunListener listener,
 			listener.failed(context, exception);
 		}
 		catch (Throwable ex) {
-			if (exception == null) {
-				ReflectionUtils.rethrowRuntimeException(ex);
-			}
 			if (this.log.isDebugEnabled()) {
 				this.log.error("Error handling failed", ex);
 			}
diff --git a/core/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionHandler.java b/core/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionHandler.java
index b29ed796ab5..b01c98c4cec 100644
--- a/core/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionHandler.java
+++ b/core/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionHandler.java
@@ -19,8 +19,6 @@
 import java.lang.Thread.UncaughtExceptionHandler;
 import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -34,13 +32,7 @@
  */
 class SpringBootExceptionHandler implements UncaughtExceptionHandler {
 
-	private static final Set<String> LOG_CONFIGURATION_MESSAGES;
-
-	static {
-		Set<String> messages = new HashSet<>();
-		messages.add("Logback configuration error detected");
-		LOG_CONFIGURATION_MESSAGES = Collections.unmodifiableSet(messages);
-	}
+	private static final Set<String> LOG_CONFIGURATION_MESSAGES = Set.of("Logback configuration error detected");
 
 	private static final LoggedExceptionHandlerThreadLocal handler = new LoggedExceptionHandlerThreadLocal();