StringUtils.toStringArray/CollectionUtils.toIterator handle null input

Closes gh-22547

spring-core/src/main/java/org/springframework/util/CollectionUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -369,12 +369,12 @@ public abstract class CollectionUtils {
 	}
 
 	/**
-	 * Adapt an enumeration to an iterator.
-	 * @param enumeration the enumeration
-	 * @return the iterator
+	 * Adapt an {@link Enumeration} to an {@link Iterator}.
+	 * @param enumeration the original {@code Enumeration}
+	 * @return the adapted {@code Iterator}
 	 */
-	public static <E> Iterator<E> toIterator(Enumeration<E> enumeration) {
-		return new EnumerationIterator<>(enumeration);
+	public static <E> Iterator<E> toIterator(@Nullable Enumeration<E> enumeration) {
+		return (enumeration != null ? new EnumerationIterator<>(enumeration) : Collections.emptyIterator());
 	}
 
 	/**
@@ -557,7 +557,7 @@ public abstract class CollectionUtils {
 			if (this == other) {
 				return true;
 			}
-			return map.equals(other);
+			return this.map.equals(other);
 		}
 
 		@Override

spring-core/src/main/java/org/springframework/util/StringUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -871,6 +871,28 @@ public abstract class StringUtils {
 	// Convenience methods for working with String arrays
 	//---------------------------------------------------------------------
 
+	/**
+	 * Copy the given {@link Collection} into a {@code String} array.
+	 * <p>The {@code Collection} must contain {@code String} elements only.
+	 * @param collection the {@code Collection} to copy
+	 * (potentially {@code null} or empty)
+	 * @return the resulting {@code String} array
+	 */
+	public static String[] toStringArray(@Nullable Collection<String> collection) {
+		return (collection != null ? collection.toArray(new String[0]) : new String[0]);
+	}
+
+	/**
+	 * Copy the given {@link Enumeration} into a {@code String} array.
+	 * <p>The {@code Enumeration} must contain {@code String} elements only.
+	 * @param enumeration the {@code Enumeration} to copy
+	 * (potentially {@code null} or empty)
+	 * @return the resulting {@code String} array
+	 */
+	public static String[] toStringArray(@Nullable Enumeration<String> enumeration) {
+		return (enumeration != null ? toStringArray(Collections.list(enumeration)) : new String[0]);
+	}
+
 	/**
 	 * Append the given {@code String} to the given {@code String} array,
 	 * returning a new array consisting of the input array contents plus
@@ -946,9 +968,9 @@ public abstract class StringUtils {
 	}
 
 	/**
-	 * Turn given source {@code String} array into sorted array.
-	 * @param array the source array
-	 * @return the sorted array (never {@code null})
+	 * Sort the given {@code String} array if necessary.
+	 * @param array the original array (potentially empty)
+	 * @return the array in sorted form (never {@code null})
 	 */
 	public static String[] sortStringArray(String[] array) {
 		if (ObjectUtils.isEmpty(array)) {
@@ -959,26 +981,6 @@ public abstract class StringUtils {
 		return array;
 	}
 
-	/**
-	 * Copy the given {@code Collection} into a {@code String} array.
-	 * <p>The {@code Collection} must contain {@code String} elements only.
-	 * @param collection the {@code Collection} to copy
-	 * @return the {@code String} array
-	 */
-	public static String[] toStringArray(Collection<String> collection) {
-		return collection.toArray(new String[0]);
-	}
-
-	/**
-	 * Copy the given Enumeration into a {@code String} array.
-	 * The Enumeration must contain {@code String} elements only.
-	 * @param enumeration the Enumeration to copy
-	 * @return the {@code String} array
-	 */
-	public static String[] toStringArray(Enumeration<String> enumeration) {
-		return toStringArray(Collections.list(enumeration));
-	}
-
 	/**
 	 * Trim the elements of the given {@code String} array,
 	 * calling {@code String.trim()} on each of them.