SPR-7209: parsing poorly formed Elvis expressions

org.springframework.expression/src/main/java/org/springframework/expression/spel/ast/Elvis.java

@@ -42,7 +42,7 @@ public class Elvis extends SpelNodeImpl {
 	@Override
 	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
 		TypedValue value = children[0].getValueInternal(state);
-		if (value.getValue()!=null) {
+		if (value.getValue()!=null && !((value.getValue() instanceof String) && ((String)value.getValue()).length()==0)) {
 			return value;
 		} else {
 			return children[1].getValueInternal(state);

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

@@ -135,14 +135,26 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 		if (moreTokens()) {
 			Token t = peekToken();
 			if (t.kind==TokenKind.ASSIGN) { // a=b
+				if (expr==null) {
+				expr = new NullLiteral(toPos(t.startpos-1,t.endpos-1));
+			}
 				nextToken();
 				SpelNodeImpl assignedValue = eatLogicalOrExpression();
 				return new Assign(toPos(t),expr,assignedValue);
 			} else if (t.kind==TokenKind.ELVIS) { // a?:b (a if it isn't null, otherwise b)
+				if (expr==null) {
+					expr = new NullLiteral(toPos(t.startpos-1,t.endpos-2));
+				}
 				nextToken(); // elvis has left the building
 				SpelNodeImpl valueIfNull = eatExpression();
+				if (valueIfNull==null) {
+					valueIfNull = new NullLiteral(toPos(t.startpos+1,t.endpos+1));
+				}
 				return new Elvis(toPos(t),expr,valueIfNull);
 			} else if (t.kind==TokenKind.QMARK) { // a?b:c
+				if (expr==null) {
+					expr = new NullLiteral(toPos(t.startpos-1,t.endpos-1));
+				}
 				nextToken();
 				SpelNodeImpl ifTrueExprValue = eatExpression();	
 				eatToken(TokenKind.COLON);

org.springframework.expression/src/test/java/org/springframework/expression/spel/SpringEL300Tests.java

@@ -627,4 +627,50 @@ public class SpringEL300Tests extends ExpressionTestCase {
 	
 	// end bean resolver tests
 
+	@Test
+	public void elvis_SPR7209_1() {
+		StandardEvaluationContext eContext = new StandardEvaluationContext(new XX());
+		Expression expr = null;
+		
+		// Different parts of elvis expression are null
+		expr = new SpelExpressionParser().parseRaw("(?:'default')");
+		Assert.assertEquals("default", expr.getValue());
+		expr = new SpelExpressionParser().parseRaw("?:'default'");
+		Assert.assertEquals("default", expr.getValue());
+		expr = new SpelExpressionParser().parseRaw("?:");
+		Assert.assertEquals(null, expr.getValue());
+
+		// Different parts of ternary expression are null
+		try {
+			expr = new SpelExpressionParser().parseRaw("(?'abc':'default')");
+			expr.getValue(eContext);
+			Assert.fail();
+		} catch (SpelEvaluationException see ) {
+			Assert.assertEquals(SpelMessage.TYPE_CONVERSION_ERROR,see.getMessageCode());
+		}
+		expr = new SpelExpressionParser().parseRaw("(false?'abc':null)");
+		Assert.assertEquals(null, expr.getValue());
+
+		// Assignment
+		try {
+			expr = new SpelExpressionParser().parseRaw("(='default')");
+			expr.getValue(eContext);
+			Assert.fail();
+		} catch (SpelEvaluationException see ) {
+			Assert.assertEquals(SpelMessage.SETVALUE_NOT_SUPPORTED,see.getMessageCode());
+		}
+	}
+
+	@Test
+	public void elvis_SPR7209_2() {
+		Expression expr = null;
+		// Have empty string treated as null for elvis
+		expr = new SpelExpressionParser().parseRaw("?:'default'");
+		Assert.assertEquals("default", expr.getValue());
+		expr = new SpelExpressionParser().parseRaw("\"\"?:'default'");
+		Assert.assertEquals("default", expr.getValue());
+		expr = new SpelExpressionParser().parseRaw("''?:'default'");
+		Assert.assertEquals("default", expr.getValue());
+	}
+	
 }