diff --git a/spring-beans/src/main/java/org/springframework/beans/factory/config/YamlProcessor.java b/spring-beans/src/main/java/org/springframework/beans/factory/config/YamlProcessor.java
index badf7685b8..a5d8e79759 100644
--- a/spring-beans/src/main/java/org/springframework/beans/factory/config/YamlProcessor.java
+++ b/spring-beans/src/main/java/org/springframework/beans/factory/config/YamlProcessor.java
@@ -432,8 +432,7 @@ public abstract class YamlProcessor {
 	/**
 	 * {@link Constructor} that supports filtering of unsupported types.
 	 * <p>If an unsupported type is encountered in a YAML document, an
-	 * {@link IllegalStateException} will be thrown from {@link #getClassForName(String)}.
-	 * @since 5.1.16
+	 * {@link IllegalStateException} will be thrown from {@link #getClassForName}.
 	 */
 	private class FilteringConstructor extends Constructor {
 
diff --git a/spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java b/spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java
index bcb11ef4b6..595ba3d942 100644
--- a/spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java
+++ b/spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -79,6 +79,7 @@ import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
 import org.springframework.core.io.support.ResourcePatternResolver;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.ReflectionUtils;
 
@@ -835,7 +836,7 @@ public abstract class AbstractApplicationContext extends DefaultResourceLoader
 		// Publish early application events now that we finally have a multicaster...
 		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
 		this.earlyApplicationEvents = null;
-		if (earlyEventsToProcess != null) {
+		if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
 			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
 				getApplicationEventMulticaster().multicastEvent(earlyEvent);
 			}
diff --git a/spring-core/src/main/java/org/springframework/core/env/AbstractPropertyResolver.java b/spring-core/src/main/java/org/springframework/core/env/AbstractPropertyResolver.java
index 7c9c68b47c..c3f29e106a 100644
--- a/spring-core/src/main/java/org/springframework/core/env/AbstractPropertyResolver.java
+++ b/spring-core/src/main/java/org/springframework/core/env/AbstractPropertyResolver.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.core.env;
 
+import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
@@ -136,9 +137,7 @@ public abstract class AbstractPropertyResolver implements ConfigurablePropertyRe
 
 	@Override
 	public void setRequiredProperties(String... requiredProperties) {
-		for (String key : requiredProperties) {
-			this.requiredProperties.add(key);
-		}
+		Collections.addAll(this.requiredProperties, requiredProperties);
 	}
 
 	@Override
@@ -224,6 +223,9 @@ public abstract class AbstractPropertyResolver implements ConfigurablePropertyRe
 	 * @see #setIgnoreUnresolvableNestedPlaceholders
 	 */
 	protected String resolveNestedPlaceholders(String value) {
+		if (value.isEmpty()) {
+			return value;
+		}
 		return (this.ignoreUnresolvableNestedPlaceholders ?
 				resolvePlaceholders(value) : resolveRequiredPlaceholders(value));
 	}
diff --git a/spring-core/src/main/java/org/springframework/core/env/EnumerablePropertySource.java b/spring-core/src/main/java/org/springframework/core/env/EnumerablePropertySource.java
index 0ef6ce4a77..2c1386d312 100644
--- a/spring-core/src/main/java/org/springframework/core/env/EnumerablePropertySource.java
+++ b/spring-core/src/main/java/org/springframework/core/env/EnumerablePropertySource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -44,10 +44,20 @@ import org.springframework.util.ObjectUtils;
  */
 public abstract class EnumerablePropertySource<T> extends PropertySource<T> {
 
+	/**
+	 * Create a new {@code EnumerablePropertySource} with the given name and source object.
+	 * @param name the associated name
+	 * @param source the source object
+	 */
 	public EnumerablePropertySource(String name, T source) {
 		super(name, source);
 	}
 
+	/**
+	 * Create a new {@code EnumerablePropertySource} with the given name and with a new
+	 * {@code Object} instance as the underlying source.
+	 * @param name the associated name
+	 */
 	protected EnumerablePropertySource(String name) {
 		super(name);
 	}
diff --git a/spring-core/src/main/java/org/springframework/core/env/MapPropertySource.java b/spring-core/src/main/java/org/springframework/core/env/MapPropertySource.java
index d08c6fb278..36597a5b24 100644
--- a/spring-core/src/main/java/org/springframework/core/env/MapPropertySource.java
+++ b/spring-core/src/main/java/org/springframework/core/env/MapPropertySource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -23,6 +23,8 @@ import org.springframework.util.StringUtils;
 
 /**
  * {@link PropertySource} that reads keys and values from a {@code Map} object.
+ * The underlying map should not contain any {@code null} values in order to
+ * comply with {@link #getProperty} and {@link #containsProperty} semantics.
  *
  * @author Chris Beams
  * @author Juergen Hoeller
@@ -31,6 +33,12 @@ import org.springframework.util.StringUtils;
  */
 public class MapPropertySource extends EnumerablePropertySource<Map<String, Object>> {
 
+	/**
+	 * Create a new {@code MapPropertySource} with the given name and {@code Map}.
+	 * @param name the associated name
+	 * @param source the Map source (without {@code null} values in order to get
+	 * consistent {@link #getProperty} and {@link #containsProperty} behavior)
+	 */
 	public MapPropertySource(String name, Map<String, Object> source) {
 		super(name, source);
 	}
diff --git a/spring-core/src/main/java/org/springframework/core/env/PropertyResolver.java b/spring-core/src/main/java/org/springframework/core/env/PropertyResolver.java
index 5554463c44..173a1a3378 100644
--- a/spring-core/src/main/java/org/springframework/core/env/PropertyResolver.java
+++ b/spring-core/src/main/java/org/springframework/core/env/PropertyResolver.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -98,7 +98,6 @@ public interface PropertyResolver {
 	 * @return the resolved String (never {@code null})
 	 * @throws IllegalArgumentException if given text is {@code null}
 	 * @see #resolveRequiredPlaceholders
-	 * @see org.springframework.util.SystemPropertyUtils#resolvePlaceholders(String)
 	 */
 	String resolvePlaceholders(String text);
 
@@ -109,7 +108,6 @@ public interface PropertyResolver {
 	 * @return the resolved String (never {@code null})
 	 * @throws IllegalArgumentException if given text is {@code null}
 	 * or if any placeholders are unresolvable
-	 * @see org.springframework.util.SystemPropertyUtils#resolvePlaceholders(String, boolean)
 	 */
 	String resolveRequiredPlaceholders(String text) throws IllegalArgumentException;
 
diff --git a/spring-core/src/main/java/org/springframework/core/env/PropertySource.java b/spring-core/src/main/java/org/springframework/core/env/PropertySource.java
index 384964df91..112fc1350b 100644
--- a/spring-core/src/main/java/org/springframework/core/env/PropertySource.java
+++ b/spring-core/src/main/java/org/springframework/core/env/PropertySource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -68,6 +68,8 @@ public abstract class PropertySource<T> {
 
 	/**
 	 * Create a new {@code PropertySource} with the given name and source object.
+	 * @param name the associated name
+	 * @param source the source object
 	 */
 	public PropertySource(String name, T source) {
 		Assert.hasText(name, "Property source name must contain at least one character");
diff --git a/spring-core/src/main/java/org/springframework/util/SystemPropertyUtils.java b/spring-core/src/main/java/org/springframework/util/SystemPropertyUtils.java
index c1769c6b63..7c5ac6bdf4 100644
--- a/spring-core/src/main/java/org/springframework/util/SystemPropertyUtils.java
+++ b/spring-core/src/main/java/org/springframework/util/SystemPropertyUtils.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -78,6 +78,9 @@ public abstract class SystemPropertyUtils {
 	 * and the "ignoreUnresolvablePlaceholders" flag is {@code false}
 	 */
 	public static String resolvePlaceholders(String text, boolean ignoreUnresolvablePlaceholders) {
+		if (text.isEmpty()) {
+			return text;
+		}
 		PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper);
 		return helper.replacePlaceholders(text, new SystemPropertyPlaceholderResolver(text));
 	}
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/JdbcOperations.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/JdbcOperations.java
index dc559b03d5..5051ec3e32 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/JdbcOperations.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/JdbcOperations.java
@@ -896,6 +896,8 @@ public interface JdbcOperations {
 	 * @param pss object to set parameters on the PreparedStatement
 	 * created by this method
 	 * @return an array of the number of rows affected by each statement
+	 * (may also contain special JDBC-defined negative values for affected rows such as
+	 * {@link java.sql.Statement#SUCCESS_NO_INFO}/{@link java.sql.Statement#EXECUTE_FAILED})
 	 * @throws DataAccessException if there is any problem issuing the update
 	 */
 	int[] batchUpdate(String sql, BatchPreparedStatementSetter pss) throws DataAccessException;
@@ -905,6 +907,8 @@ public interface JdbcOperations {
 	 * @param sql the SQL statement to execute
 	 * @param batchArgs the List of Object arrays containing the batch of arguments for the query
 	 * @return an array containing the numbers of rows affected by each update in the batch
+	 * (may also contain special JDBC-defined negative values for affected rows such as
+	 * {@link java.sql.Statement#SUCCESS_NO_INFO}/{@link java.sql.Statement#EXECUTE_FAILED})
 	 * @throws DataAccessException if there is any problem issuing the update
 	 */
 	int[] batchUpdate(String sql, List<Object[]> batchArgs) throws DataAccessException;
@@ -916,20 +920,24 @@ public interface JdbcOperations {
 	 * @param argTypes the SQL types of the arguments
 	 * (constants from {@code java.sql.Types})
 	 * @return an array containing the numbers of rows affected by each update in the batch
+	 * (may also contain special JDBC-defined negative values for affected rows such as
+	 * {@link java.sql.Statement#SUCCESS_NO_INFO}/{@link java.sql.Statement#EXECUTE_FAILED})
 	 * @throws DataAccessException if there is any problem issuing the update
 	 */
 	int[] batchUpdate(String sql, List<Object[]> batchArgs, int[] argTypes) throws DataAccessException;
 
 	/**
-	 * Execute multiple batches using the supplied SQL statement with the collect of supplied arguments.
-	 * The arguments' values will be set using the ParameterizedPreparedStatementSetter.
+	 * Execute multiple batches using the supplied SQL statement with the collect of supplied
+	 * arguments. The arguments' values will be set using the ParameterizedPreparedStatementSetter.
 	 * Each batch should be of size indicated in 'batchSize'.
 	 * @param sql the SQL statement to execute.
 	 * @param batchArgs the List of Object arrays containing the batch of arguments for the query
 	 * @param batchSize batch size
 	 * @param pss the ParameterizedPreparedStatementSetter to use
-	 * @return an array containing for each batch another array containing the numbers of rows affected
-	 * by each update in the batch
+	 * @return an array containing for each batch another array containing the numbers of
+	 * rows affected by each update in the batch
+	 * (may also contain special JDBC-defined negative values for affected rows such as
+	 * {@link java.sql.Statement#SUCCESS_NO_INFO}/{@link java.sql.Statement#EXECUTE_FAILED})
 	 * @throws DataAccessException if there is any problem issuing the update
 	 * @since 3.1
 	 */
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/NamedParameterJdbcOperations.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/NamedParameterJdbcOperations.java
index d37abe95c1..c2879549b6 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/NamedParameterJdbcOperations.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/NamedParameterJdbcOperations.java
@@ -498,6 +498,8 @@ public interface NamedParameterJdbcOperations {
 	 * @param sql the SQL statement to execute
 	 * @param batchValues the array of Maps containing the batch of arguments for the query
 	 * @return an array containing the numbers of rows affected by each update in the batch
+	 * (may also contain special JDBC-defined negative values for affected rows such as
+	 * {@link java.sql.Statement#SUCCESS_NO_INFO}/{@link java.sql.Statement#EXECUTE_FAILED})
 	 * @throws DataAccessException if there is any problem issuing the update
 	 */
 	int[] batchUpdate(String sql, Map<String, ?>[] batchValues);
@@ -505,8 +507,11 @@ public interface NamedParameterJdbcOperations {
 	/**
 	 * Execute a batch using the supplied SQL statement with the batch of supplied arguments.
 	 * @param sql the SQL statement to execute
-	 * @param batchArgs the array of {@link SqlParameterSource} containing the batch of arguments for the query
+	 * @param batchArgs the array of {@link SqlParameterSource} containing the batch of
+	 * arguments for the query
 	 * @return an array containing the numbers of rows affected by each update in the batch
+	 * (may also contain special JDBC-defined negative values for affected rows such as
+	 * {@link java.sql.Statement#SUCCESS_NO_INFO}/{@link java.sql.Statement#EXECUTE_FAILED})
 	 * @throws DataAccessException if there is any problem issuing the update
 	 */
 	int[] batchUpdate(String sql, SqlParameterSource[] batchArgs);
diff --git a/spring-orm/src/main/java/org/springframework/orm/hibernate5/support/OpenSessionInViewFilter.java b/spring-orm/src/main/java/org/springframework/orm/hibernate5/support/OpenSessionInViewFilter.java
index a68af6f778..ec23f51c02 100644
--- a/spring-orm/src/main/java/org/springframework/orm/hibernate5/support/OpenSessionInViewFilter.java
+++ b/spring-orm/src/main/java/org/springframework/orm/hibernate5/support/OpenSessionInViewFilter.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -51,11 +51,11 @@ import org.springframework.web.filter.OncePerRequestFilter;
  * as well as for non-transactional execution (if configured appropriately).
  *
  * <p><b>NOTE</b>: This filter will by default <i>not</i> flush the Hibernate Session,
- * with the flush mode set to {@code FlushMode.NEVER}. It assumes to be used
+ * with the flush mode set to {@code FlushMode.MANUAL}. It assumes to be used
  * in combination with service layer transactions that care for the flushing: The
  * active transaction manager will temporarily change the flush mode to
  * {@code FlushMode.AUTO} during a read-write transaction, with the flush
- * mode reset to {@code FlushMode.NEVER} at the end of each transaction.
+ * mode reset to {@code FlushMode.MANUAL} at the end of each transaction.
  *
  * <p><b>WARNING:</b> Applying this filter to existing logic can cause issues that
  * have not appeared before, through the use of a single Hibernate Session for the
diff --git a/spring-tx/src/main/java/org/springframework/transaction/support/TransactionSynchronizationManager.java b/spring-tx/src/main/java/org/springframework/transaction/support/TransactionSynchronizationManager.java
index 19f20f8571..df9132d13d 100644
--- a/spring-tx/src/main/java/org/springframework/transaction/support/TransactionSynchronizationManager.java
+++ b/spring-tx/src/main/java/org/springframework/transaction/support/TransactionSynchronizationManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -383,7 +383,7 @@ public abstract class TransactionSynchronizationManager {
 	 * as argument for the {@code beforeCommit} callback, to be able
 	 * to suppress change detection on commit. The present method is meant
 	 * to be used for earlier read-only checks, for example to set the
-	 * flush mode of a Hibernate Session to "FlushMode.NEVER" upfront.
+	 * flush mode of a Hibernate Session to "FlushMode.MANUAL" upfront.
 	 * @see org.springframework.transaction.TransactionDefinition#isReadOnly()
 	 * @see TransactionSynchronization#beforeCommit(boolean)
 	 */
diff --git a/spring-web/src/main/java/org/springframework/web/util/ServletContextPropertyUtils.java b/spring-web/src/main/java/org/springframework/web/util/ServletContextPropertyUtils.java
index 18709788aa..ffaefa75b4 100644
--- a/spring-web/src/main/java/org/springframework/web/util/ServletContextPropertyUtils.java
+++ b/spring-web/src/main/java/org/springframework/web/util/ServletContextPropertyUtils.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.web.util;
 
 import javax.servlet.ServletContext;
@@ -73,16 +74,18 @@ public abstract class ServletContextPropertyUtils {
 	 * @see SystemPropertyUtils#PLACEHOLDER_SUFFIX
 	 * @see SystemPropertyUtils#resolvePlaceholders(String, boolean)
 	 */
-	public static String resolvePlaceholders(String text, ServletContext servletContext,
-			boolean ignoreUnresolvablePlaceholders) {
+	public static String resolvePlaceholders(
+			String text, ServletContext servletContext, boolean ignoreUnresolvablePlaceholders) {
 
+		if (text.isEmpty()) {
+			return text;
+		}
 		PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper);
 		return helper.replacePlaceholders(text, new ServletContextPlaceholderResolver(text, servletContext));
 	}
 
 
-	private static class ServletContextPlaceholderResolver
-			implements PropertyPlaceholderHelper.PlaceholderResolver {
+	private static class ServletContextPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver {
 
 		private final String text;