Revert changes on PropertParser for applying review comment of gh-2886

Author: kazuki43zoo

src/main/java/org/apache/ibatis/builder/annotation/MapperAnnotationBuilder.java

@@ -381,10 +381,9 @@ private <T> T parseStringValue(String valueString, T fallbackValue, Function<Str
     if (valueString.isEmpty()) {
       return fallbackValue;
     } else {
-      Properties defaults = new Properties();
+      Properties variables = new Properties();
       Optional.ofNullable(fallbackValue).map(String::valueOf)
-          .ifPresent(x -> defaults.setProperty(TOKEN_PARSER.parse(valueString), x));
-      Properties variables = new Properties(defaults);
+          .ifPresent(x -> variables.setProperty(TOKEN_PARSER.parse(valueString), x));
       variables.putAll(configuration.getVariables());
       return Optional.ofNullable(PropertyParser.parse(valueString, variables)).map(valueTypeConverter)
           .orElse(fallbackValue);

src/main/java/org/apache/ibatis/parsing/PropertyParser.java

@@ -88,9 +88,8 @@ public String handleToken(String content) {
             return variables.getProperty(key, defaultValue);
           }
         }
-        String value = variables.getProperty(key);
-        if (value != null) {
-          return value;
+        if (variables.containsKey(key)) {
+          return variables.getProperty(key);
         }
       }
       return "${" + content + "}";