TemplateAwareExpressionParser treats null as non-template ParserContext

Issue: SPR-15810

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

@@ -54,11 +54,16 @@ public interface ParserContext {
 
 
 	/**
-	 * The default ParserContext implementation that enables template expression parsing
-	 * mode. The expression prefix is #{ and the expression suffix is }.
+	 * The default ParserContext implementation that enables template expression
+	 * parsing mode. The expression prefix is "#{" and the expression suffix is "}".
 	 * @see #isTemplate()
 	 */
-	public static final ParserContext TEMPLATE_EXPRESSION = new ParserContext() {
+	ParserContext TEMPLATE_EXPRESSION = new ParserContext() {
+
+		@Override
+		public boolean isTemplate() {
+			return true;
+		}
 
 		@Override
 		public String getExpressionPrefix() {
@@ -69,12 +74,6 @@ public interface ParserContext {
 		public String getExpressionSuffix() {
 			return "}";
 		}
-
-		@Override
-		public boolean isTemplate() {
-			return true;
-		}
-
 	};
 
 }

spring-expression/src/main/java/org/springframework/expression/common/TemplateAwareExpressionParser.java

@@ -37,33 +37,14 @@ import org.springframework.lang.Nullable;
  */
 public abstract class TemplateAwareExpressionParser implements ExpressionParser {
 
-	/**
-	 * Default ParserContext instance for non-template expressions.
-	 */
-	private static final ParserContext NON_TEMPLATE_PARSER_CONTEXT = new ParserContext() {
-		@Override
-		public boolean isTemplate() {
-			return false;
-		}
-		@Override
-		public String getExpressionPrefix() {
-			return "";
-		}
-		@Override
-		public String getExpressionSuffix() {
-			return "";
-		}
-	};
-
-
 	@Override
 	public Expression parseExpression(String expressionString) throws ParseException {
-		return parseExpression(expressionString, NON_TEMPLATE_PARSER_CONTEXT);
+		return parseExpression(expressionString, null);
 	}
 
 	@Override
-	public Expression parseExpression(String expressionString, ParserContext context) throws ParseException {
-		if (context.isTemplate()) {
+	public Expression parseExpression(String expressionString, @Nullable ParserContext context) throws ParseException {
+		if (context != null && context.isTemplate()) {
 			return parseTemplate(expressionString, context);
 		}
 		else {