Polishing

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 {
 
@@ -441,7 +440,6 @@ public abstract class YamlProcessor {
 			super(loaderOptions);
 		}
 
-
 		@Override
 		protected Class<?> getClassForName(String name) throws ClassNotFoundException {
 			Assert.state(YamlProcessor.this.supportedTypes.contains(name),

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.
@@ -223,6 +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));
 	}

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);
 	}

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;
 

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");

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));
 	}

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;