Polish contribution

See gh-25367

Author: sbrannen

spring-expression/src/main/java/org/springframework/expression/spel/ast/Indexer.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.
@@ -712,10 +712,11 @@ private void growCollectionIfNecessary() {
 				}
 				TypeDescriptor elementType = this.collectionEntryDescriptor.getElementTypeDescriptor();
 				try {
-					Constructor<?> ctor = getConstructor(elementType.getType());
+					Constructor<?> ctor = getDefaultConstructor(elementType.getType());
 					int newElements = this.index - this.collection.size();
 					while (newElements >= 0) {
-						this.collection.add(ctor == null ? null : ctor.newInstance());
+						// Insert a null value if the element type does not have a default constructor.
+						this.collection.add(ctor != null ? ctor.newInstance() : null);
 						newElements--;
 					}
 				}
@@ -725,7 +726,7 @@ private void growCollectionIfNecessary() {
 			}
 		}
 
-		Constructor<?> getConstructor(Class<?> type) {
+		private Constructor<?> getDefaultConstructor(Class<?> type) {
 			try {
 				return ReflectionUtils.accessibleConstructor(type);
 			}

spring-expression/src/test/java/org/springframework/expression/spel/IndexingTests.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.
@@ -203,22 +203,21 @@ public void setGenericPropertyContainingListAutogrow() {
 	public List<BigDecimal> decimals;
 
 	@Test
-	public void autoGrowWithoutDefaultConstructor() {
+	public void autoGrowListOfElementsWithoutDefaultConstructor() {
 		this.decimals = new ArrayList<>();
 		SpelExpressionParser parser = new SpelExpressionParser(new SpelParserConfiguration(true, true));
 		parser.parseExpression("decimals[0]").setValue(this, "123.4");
-		assertThat(decimals.get(0)).isEqualTo(BigDecimal.valueOf(123.4));
+		assertThat(decimals).containsExactly(BigDecimal.valueOf(123.4));
 	}
 
 	@Test
-	public void indexIntoPropertyContainingNullList() {
+	public void indexIntoPropertyContainingListContainingNullElement() {
 		this.decimals = new ArrayList<>();
 		this.decimals.add(null);
 		this.decimals.add(BigDecimal.ONE);
 		SpelExpressionParser parser = new SpelExpressionParser(new SpelParserConfiguration(true, true));
 		parser.parseExpression("decimals[0]").setValue(this, "9876.5");
-		assertThat(decimals.get(0)).isEqualTo(BigDecimal.valueOf(9876.5));
-		assertThat(decimals.get(1)).isEqualTo(BigDecimal.ONE);
+		assertThat(decimals).containsExactly(BigDecimal.valueOf(9876.5), BigDecimal.ONE);
 	}
 
 	@Test

src/docs/asciidoc/core/core-expressions.adoc

@@ -332,19 +332,20 @@ being placed in it. The following example shows how to do so:
 [[expressions-parser-configuration]]
 === Parser Configuration
 
-It is possible to configure the SpEL expression parser by using a parser configuration object
-(`org.springframework.expression.spel.SpelParserConfiguration`). The configuration
+It is possible to configure the SpEL expression parser by using a parser configuration
+object (`org.springframework.expression.spel.SpelParserConfiguration`). The configuration
 object controls the behavior of some of the expression components. For example, if you
-index into an array or collection and the element at the specified index is `null`,
-you can automatically create the element. This is useful when using expressions made up of a
-chain of property references. If you index into an array or list
-and specifying an index that is beyond the end of the current size of the array or
-list, you can automatically grow the array or list to accommodate that index. In order to add
-an element at the specified index, SpEL will try to create the element using a default
-constructor before setting the specified value. If the element type does not have a default
-constructor, `null` will be added. Note if there is no built-in or custom converter, that knows
-how to set the value, `null` will remain in the array or list at the specified index.
-The following example demonstrates how to automatically grow the list:
+index into an array or collection and the element at the specified index is `null`, SpEL
+can automatically create the element. This is useful when using expressions made up of a
+chain of property references. If you index into an array or list and specify an index
+that is beyond the end of the current size of the array or list, SpEL can automatically
+grow the array or list to accommodate that index. In order to add an element at the
+specified index, SpEL will try to create the element using the element type's default
+constructor before setting the specified value. If the element type does not have a
+default constructor, `null` will be added to the array or list. If there is no built-in
+or custom converter that knows how to set the value, `null` will remain in the array or
+list at the specified index. The following example demonstrates how to automatically grow
+the list:
 
 [source,java,indent=0,subs="verbatim,quotes",role="primary"]
 .Java