diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/Assign.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/Assign.java
index 4b0398760ad..3289c66f5bb 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/Assign.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/Assign.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -21,8 +21,8 @@ import org.springframework.expression.TypedValue;
 import org.springframework.expression.spel.ExpressionState;
 
 /**
- * Represents assignment. An alternative to calling setValue() for an expression is to use
- * an assign.
+ * Represents assignment. An alternative to calling {@code setValue}
+ * for an expression which indicates an assign statement.
  *
  * <p>Example: 'someNumberProperty=42'
  *
@@ -31,8 +31,8 @@ import org.springframework.expression.spel.ExpressionState;
  */
 public class Assign extends SpelNodeImpl {
 
-	public Assign(int pos,SpelNodeImpl... operands) {
-		super(pos,operands);
+	public Assign(int pos, SpelNodeImpl... operands) {
+		super(pos, operands);
 	}
 
 
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java
index aed04c557fe..0cebe564494 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java
@@ -47,7 +47,7 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 	private static final SpelNodeImpl[] NO_CHILDREN = new SpelNodeImpl[0];
 
 
-	protected int pos;  // start = top 16bits, end = bottom 16bits
+	protected final int pos;  // start = top 16bits, end = bottom 16bits
 
 	protected SpelNodeImpl[] children = SpelNodeImpl.NO_CHILDREN;
 
@@ -69,8 +69,6 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 
 	public SpelNodeImpl(int pos, SpelNodeImpl... operands) {
 		this.pos = pos;
-		// pos combines start and end so can never be zero because tokens cannot be zero length
-		Assert.isTrue(pos != 0, "Pos must not be 0");
 		if (!ObjectUtils.isEmpty(operands)) {
 			this.children = operands;
 			for (SpelNodeImpl operand : operands) {
@@ -84,7 +82,7 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 	/**
      * Return {@code true} if the next child is one of the specified classes.
      */
-	protected boolean nextChildIs(Class<?>... clazzes) {
+	protected boolean nextChildIs(Class<?>... classes) {
 		if (this.parent != null) {
 			SpelNodeImpl[] peers = this.parent.children;
 			for (int i = 0, max = peers.length; i < max; i++) {
@@ -92,9 +90,9 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 					if (i + 1 >= max) {
 						return false;
 					}
-					Class<?> clazz = peers[i + 1].getClass();
-					for (Class<?> desiredClazz : clazzes) {
-						if (clazz.equals(desiredClazz)) {
+					Class<?> peerClass = peers[i + 1].getClass();
+					for (Class<?> desiredClass : classes) {
+						if (peerClass == desiredClass) {
 							return true;
 						}
 					}
@@ -146,11 +144,6 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 		return (obj instanceof Class ? ((Class<?>) obj) : obj.getClass());
 	}
 
-	@Nullable
-	protected final <T> T getValue(ExpressionState state, Class<T> desiredReturnType) throws EvaluationException {
-		return ExpressionUtils.convertTypedValue(state.getEvaluationContext(), getValueInternal(state), desiredReturnType);
-	}
-
 	@Override
 	public int getStartPosition() {
 		return (this.pos >> 16);
@@ -161,10 +154,6 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 		return (this.pos & 0xffff);
 	}
 
-	protected ValueRef getValueRef(ExpressionState state) throws EvaluationException {
-		throw new SpelEvaluationException(this.pos, SpelMessage.NOT_ASSIGNABLE, toStringAST());
-	}
-
 	/**
 	 * Check whether a node can be compiled to bytecode. The reasoning in each node may
 	 * be different but will typically involve checking whether the exit type descriptor
@@ -177,9 +166,8 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 
 	/**
 	 * Generate the bytecode for this node into the supplied visitor. Context info about
-	 * the current expression being compiled is available in the codeflow object. For
-	 * example it will include information about the type of the object currently
-	 * on the stack.
+	 * the current expression being compiled is available in the codeflow object, e.g.
+	 * including information about the type of the object currently on the stack.
 	 * @param mv the ASM MethodVisitor into which code should be generated
 	 * @param cf a context object with info about what is on the stack
 	 */
@@ -192,6 +180,15 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 		return this.exitTypeDescriptor;
 	}
 
+	@Nullable
+	protected final <T> T getValue(ExpressionState state, Class<T> desiredReturnType) throws EvaluationException {
+		return ExpressionUtils.convertTypedValue(state.getEvaluationContext(), getValueInternal(state), desiredReturnType);
+	}
+
+	protected ValueRef getValueRef(ExpressionState state) throws EvaluationException {
+		throw new SpelEvaluationException(getStartPosition(), SpelMessage.NOT_ASSIGNABLE, toStringAST());
+	}
+
 	public abstract TypedValue getValueInternal(ExpressionState expressionState) throws EvaluationException;