Refine null-safety in the spring-expression module

Closes gh-34156

Author: sdeleuze

spring-expression/src/main/java/org/springframework/expression/ExpressionException.java

@@ -153,7 +153,7 @@ public String toDetailedString() {
 	 * that caused the failure.
 	 * @since 4.0
 	 */
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	public String getSimpleMessage() {
 		return super.getMessage();
 	}

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

@@ -174,7 +174,6 @@ private TypedValue executeFunctionViaMethod(ExpressionState state, Method method
 	 * @throws EvaluationException if there is any problem invoking the method
 	 * @since 6.1
 	 */
-	@SuppressWarnings("NullAway") // TODO Remove when NullAway 0.12.2 is released, see https://github.com/uber/NullAway/pull/1089
 	private TypedValue executeFunctionViaMethodHandle(ExpressionState state, MethodHandle methodHandle) throws EvaluationException {
 		Object[] functionArgs = getArguments(state);
 		MethodType declaredParams = methodHandle.type();

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

@@ -351,7 +351,7 @@ private DescriptorComparison(boolean areNumbers, boolean areCompatible, char com
 		 * @param rightActualDescriptor the dynamic/runtime right object descriptor
 		 * @return a DescriptorComparison object indicating the type of compatibility, if any
 		 */
-		@SuppressWarnings("NullAway")
+		@SuppressWarnings("NullAway") // Dataflow analysis limitation
 		public static DescriptorComparison checkNumericCompatibility(
 				@Nullable String leftDeclaredDescriptor, @Nullable String rightDeclaredDescriptor,
 				@Nullable String leftActualDescriptor, @Nullable String rightActualDescriptor) {

spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java

@@ -166,7 +166,7 @@ private void checkExpressionLength(String string) {
 	//	    | (DEFAULT^ logicalOrExpression)
 	//	    | (QMARK^ expression COLON! expression)
 	//      | (ELVIS^ expression))?;
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Not null assertion performed in SpelNodeImpl constructor
 	private @Nullable SpelNodeImpl eatExpression() {
 		SpelNodeImpl expr = eatLogicalOrExpression();
 		Token t = peekToken();
@@ -273,7 +273,7 @@ private void checkExpressionLength(String string) {
 	}
 
 	//sumExpression: productExpression ( (PLUS^ | MINUS^) productExpression)*;
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Not null assertion performed in SpelNodeImpl constructor
 	private @Nullable SpelNodeImpl eatSumExpression() {
 		SpelNodeImpl expr = eatProductExpression();
 		while (peekToken(TokenKind.PLUS, TokenKind.MINUS, TokenKind.INC)) {
@@ -311,7 +311,7 @@ else if (t.kind == TokenKind.MOD) {
 	}
 
 	// powerExpr  : unaryExpression (POWER^ unaryExpression)? (INC || DEC) ;
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Not null assertion performed in SpelNodeImpl constructor
 	private @Nullable SpelNodeImpl eatPowerIncDecExpression() {
 		SpelNodeImpl expr = eatUnaryExpression();
 		if (peekToken(TokenKind.POWER)) {
@@ -331,7 +331,7 @@ else if (t.kind == TokenKind.MOD) {
 	}
 
 	// unaryExpression: (PLUS^ | MINUS^ | BANG^ | INC^ | DEC^) unaryExpression | primaryExpression ;
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Not null assertion performed in SpelNodeImpl constructor
 	private @Nullable SpelNodeImpl eatUnaryExpression() {
 		if (peekToken(TokenKind.NOT, TokenKind.PLUS, TokenKind.MINUS)) {
 			Token t = takeToken();

spring-expression/src/main/java/org/springframework/expression/spel/support/ReflectivePropertyAccessor.java

@@ -154,7 +154,7 @@ public boolean canRead(EvaluationContext context, @Nullable Object target, Strin
 	}
 
 	@Override
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	public TypedValue read(EvaluationContext context, @Nullable Object target, String name) throws AccessException {
 		Assert.state(target != null, "Target must not be null");
 		Class<?> type = (target instanceof Class<?> clazz ? clazz : target.getClass());
@@ -507,7 +507,7 @@ protected String getPropertyMethodSuffix(String propertyName) {
 	 * <p>Note: An optimized accessor is currently only usable for read attempts.
 	 * Do not call this method if you need a read-write accessor.
 	 */
-	@SuppressWarnings("NullAway")
+	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	public PropertyAccessor createOptimalAccessor(EvaluationContext context, @Nullable Object target, String name) {
 		// Don't be clever for arrays or a null target...
 		if (target == null) {