CLI-313: Fixed StringIndexOutOfBoundsException for Java-like property token

Author: kumarp149

src/main/java/org/apache/commons/cli/DefaultParser.java

@@ -580,7 +580,7 @@ private boolean isArgument(final String token) {
      * Tests if the specified token is a Java-like property (-Dkey=value).
      */
     private boolean isJavaProperty(final String token) {
-        final String opt = token.substring(0, 1);
+        final String opt = token.isEmpty() ? null : token.substring(0, 1);
         final Option option = options.getOption(opt);
 
         return option != null && (option.getArgs() >= 2 || option.getArgs() == Option.UNLIMITED_VALUES);

src/test/java/org/apache/commons/cli/ParserTestCase.java

@@ -1020,5 +1020,12 @@ public void testWithRequiredOption() throws Exception {
         assertEquals("Confirm arg of -b", "file", cl.getOptionValue("b"));
         assertTrue("Confirm NO of extra args", cl.getArgList().isEmpty());
     }
-
+    
+    @Test(expected = UnrecognizedOptionException.class)
+    public void testAmbiguousArgParsing() throws Exception {
+        final String[] args = {"-=-"};
+        final Options options = new Options();
+        
+        final CommandLine cl = parser.parse(options, args);
+    }
 }