[OLINGO-1117] Sending skip and take requests without a value returns String index out of range Exception

fit/src/test/java/org/apache/olingo/fit/tecsvc/http/BasicHttpITCase.java

@@ -181,5 +181,29 @@ public class BasicHttpITCase extends AbstractBaseTestITCase {
   protected ODataClient getClient() {
     return null;
   }
+  @Test
+  public void testInvalidTopUrl() throws Exception {
+    URL url = new URL(SERVICE_URI + "?$top");
 
+    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
+    connection.setRequestMethod(HttpMethod.GET.name());
+    connection.connect();
+
+    assertEquals(HttpStatusCode.BAD_REQUEST.getStatusCode(), connection.getResponseCode());
+    assertTrue(IOUtils.toString(connection.getErrorStream()).
+        contains("The system query option '$top' has the not-allowed value ''."));
+  }
+ 
+  @Test
+  public void testInvalidSkipUrl() throws Exception {
+    URL url = new URL(SERVICE_URI + "?$skip=");
+
+    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
+    connection.setRequestMethod(HttpMethod.GET.name());
+    connection.connect();
+
+    assertEquals(HttpStatusCode.BAD_REQUEST.getStatusCode(), connection.getResponseCode());
+    assertTrue(IOUtils.toString(connection.getErrorStream()).
+        contains("The system query option '$skip' has the not-allowed value ''."));
+  }
 }

lib/server-core/src/main/java/org/apache/olingo/server/core/ODataHandlerImpl.java

@@ -211,7 +211,10 @@ public class ODataHandlerImpl implements ODataHandler {
       if(endIndex == -1) {
         endIndex = query.length();
       }
-      final String format = query.substring(index + formatOption.length(), endIndex);
+      String format = "";
+      if (index + formatOption.length() < endIndex) {
+         format = query.substring(index + formatOption.length(), endIndex);
+      }
       return new FormatOptionImpl().setFormat(format);
     }
     return uriInfo.getFormatOption();