Polishing

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));
 	}

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/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);
 	}

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));
 	}