Nullability refinements (based on IntelliJ IDEA 2018.1 introspection)

Issue: SPR-15756

spring-expression/src/main/java/org/springframework/expression/spel/CodeFlow.java

@@ -58,7 +58,7 @@ public class CodeFlow implements Opcodes {
 	 * sub-expressions like the expressions for the argument values in a method invocation
 	 * expression.
 	 */
-	private final Deque<ArrayList<String>> compilationScopes;
+	private final Deque<List<String>> compilationScopes;
 
 	/**
 	 * As SpEL ast nodes are called to generate code for the main evaluation method
@@ -128,7 +128,7 @@ public class CodeFlow implements Opcodes {
 	 */
 	public void pushDescriptor(@Nullable String descriptor) {
 		if (descriptor != null) {
-			this.compilationScopes.peek().add(descriptor);
+			this.compilationScopes.element().add(descriptor);
 		}
 	}
 

spring-expression/src/main/java/org/springframework/expression/spel/ExpressionState.java

@@ -106,7 +106,7 @@ public class ExpressionState {
 		if (CollectionUtils.isEmpty(this.contextObjects)) {
 			return this.rootObject;
 		}
-		return this.contextObjects.peek();
+		return this.contextObjects.element();
 	}
 
 	public void pushActiveContextObject(TypedValue obj) {
@@ -136,7 +136,7 @@ public class ExpressionState {
 		if (CollectionUtils.isEmpty(this.scopeRootObjects)) {
 			return this.rootObject;
 		}
-		return this.scopeRootObjects.peek();
+		return this.scopeRootObjects.element();
 	}
 
 	public void setVariable(String name, @Nullable Object value) {
@@ -157,8 +157,8 @@ public class ExpressionState {
 	}
 
 	public Object convertValue(Object value, TypeDescriptor targetTypeDescriptor) throws EvaluationException {
-		Object result = this.relatedContext.getTypeConverter().convertValue(value,
-				TypeDescriptor.forObject(value), targetTypeDescriptor);
+		Object result = this.relatedContext.getTypeConverter().convertValue(
+				value, TypeDescriptor.forObject(value), targetTypeDescriptor);
 		if (result == null) {
 			throw new IllegalStateException("Null conversion result for value [" + value + "]");
 		}
@@ -172,7 +172,8 @@ public class ExpressionState {
 	@Nullable
 	public Object convertValue(TypedValue value, TypeDescriptor targetTypeDescriptor) throws EvaluationException {
 		Object val = value.getValue();
-		return this.relatedContext.getTypeConverter().convertValue(val, TypeDescriptor.forObject(val), targetTypeDescriptor);
+		return this.relatedContext.getTypeConverter().convertValue(
+				val, TypeDescriptor.forObject(val), targetTypeDescriptor);
 	}
 
 	/*
@@ -199,7 +200,7 @@ public class ExpressionState {
 	}
 
 	public void setLocalVariable(String name, Object value) {
-		initVariableScopes().peek().setVariable(name, value);
+		initVariableScopes().element().setVariable(name, value);
 	}
 
 	@Nullable
@@ -212,16 +213,16 @@ public class ExpressionState {
 		return null;
 	}
 
-	private LinkedList<VariableScope> initVariableScopes() {
+	private Deque<VariableScope> initVariableScopes() {
 		if (this.variableScopes == null) {
 			this.variableScopes = new LinkedList<>();
-			// top level empty variable scope
+			// top-level empty variable scope
 			this.variableScopes.add(new VariableScope());
 		}
 		return this.variableScopes;
 	}
 
-	private ArrayDeque<TypedValue> initScopeRootObjects() {
+	private Deque<TypedValue> initScopeRootObjects() {
 		if (this.scopeRootObjects == null) {
 			this.scopeRootObjects = new ArrayDeque<>();
 		}

spring-expression/src/main/java/org/springframework/expression/spel/ast/ValueRef.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -58,7 +58,7 @@ public interface ValueRef {
 	/**
 	 * A ValueRef for the null value.
 	 */
-	static class NullValueRef implements ValueRef {
+	class NullValueRef implements ValueRef {
 
 		static final NullValueRef INSTANCE = new NullValueRef();
 
@@ -85,13 +85,13 @@ public interface ValueRef {
 	/**
 	 * A ValueRef holder for a single value, which cannot be set.
 	 */
-	static class TypedValueHolderValueRef implements ValueRef {
+	class TypedValueHolderValueRef implements ValueRef {
 
 		private final TypedValue typedValue;
 
 		private final SpelNodeImpl node;  // used only for error reporting
 
-		public TypedValueHolderValueRef(TypedValue typedValue,SpelNodeImpl node) {
+		public TypedValueHolderValueRef(TypedValue typedValue, SpelNodeImpl node) {
 			this.typedValue = typedValue;
 			this.node = node;
 		}