Retain null-safe syntax in AST representation of selection & projection

Prior to this commit, SpEL's CompoundExpression omitted the null-safe
syntax in AST string representations of the selection and projection
operators.

To address this, this commit implements isNullSafe() in Projection and
Selection.

Closes gh-32515

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

@@ -52,6 +52,15 @@ public class Projection extends SpelNodeImpl {
 	}
 
 
+	/**
+	 * Does this node represent a null-safe projection operation?
+	 * @since 6.1.6
+	 */
+	@Override
+	public final boolean isNullSafe() {
+		return this.nullSafe;
+	}
+
 	@Override
 	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
 		return getValueRef(state).getValue();

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

@@ -78,6 +78,15 @@ public class Selection extends SpelNodeImpl {
 	}
 
 
+	/**
+	 * Does this node represent a null-safe selection operation?
+	 * @since 6.1.6
+	 */
+	@Override
+	public final boolean isNullSafe() {
+		return this.nullSafe;
+	}
+
 	@Override
 	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
 		return getValueRef(state).getValue();

spring-expression/src/test/java/org/springframework/expression/spel/ParsingTests.java

@@ -44,9 +44,24 @@ class ParsingTests {
 
 		@Test
 		void compoundExpressions() {
+			parseCheck("#var1.methodOne().methodTwo(42)");
+			parseCheck("#func1().methodOne().methodTwo(42)");
+			parseCheck("#func2('enigma').methodOne().methodTwo(42)");
 			parseCheck("property1.property2.methodOne()");
-			parseCheck("property1[0].property2['key'].methodOne()");
+			parseCheck("property1.methodOne('enigma').methodTwo(42)");
+			parseCheck("property1.methodOne().property2.methodTwo()");
+			parseCheck("property1[0].property2['key'].methodTwo()");
+			parseCheck("property1[0][1].property2['key'][42].methodTwo()");
+
+			// null-safe variants
+			parseCheck("#var1?.methodOne()?.methodTwo(42)");
+			parseCheck("#func1()?.methodOne()?.methodTwo(42)");
+			parseCheck("#func2('enigma')?.methodOne()?.methodTwo(42)");
+			parseCheck("property1?.property2?.methodOne()");
+			parseCheck("property1?.methodOne('enigma')?.methodTwo(42)");
 			parseCheck("property1?.methodOne()?.property2?.methodTwo()");
+			parseCheck("property1[0]?.property2['key']?.methodTwo()");
+			parseCheck("property1[0][1]?.property2['key'][42]?.methodTwo()");
 		}
 
 		@Test
@@ -132,25 +147,34 @@ class ParsingTests {
 
 		@Test
 		void projection() {
-			parseCheck("{1,2,3,4,5,6,7,8,9,10}.![#isEven()]");
+			parseCheck("{1,2,3}.![#isEven()]");
+
+			// null-safe variant
+			parseCheck("{1,2,3}?.![#isEven()]");
 		}
 
 		@Test
 		void selection() {
-			parseCheck("{1,2,3,4,5,6,7,8,9,10}.?[#isEven(#this) == 'y']",
-					"{1,2,3,4,5,6,7,8,9,10}.?[(#isEven(#this) == 'y')]");
+			parseCheck("{1,2,3}.?[#isEven(#this)]");
+
+			// null-safe variant
+			parseCheck("{1,2,3}?.?[#isEven(#this)]");
 		}
 
 		@Test
-		void selectionFirst() {
-			parseCheck("{1,2,3,4,5,6,7,8,9,10}.^[#isEven(#this) == 'y']",
-					"{1,2,3,4,5,6,7,8,9,10}.^[(#isEven(#this) == 'y')]");
+		void selectFirst() {
+			parseCheck("{1,2,3}.^[#isEven(#this)]");
+
+			// null-safe variant
+			parseCheck("{1,2,3}?.^[#isEven(#this)]");
 		}
 
 		@Test
-		void selectionLast() {
-			parseCheck("{1,2,3,4,5,6,7,8,9,10}.$[#isEven(#this) == 'y']",
-					"{1,2,3,4,5,6,7,8,9,10}.$[(#isEven(#this) == 'y')]");
+		void selectLast() {
+			parseCheck("{1,2,3}.$[#isEven(#this)]");
+
+			// null-safe variant
+			parseCheck("{1,2,3}?.$[#isEven(#this)]");
 		}
 	}