Fix crash for empty properties on the url

Author: jvictorhuguenin

java/flight/flight-jdbc-driver/src/main/java/org/apache/arrow/driver/jdbc/utils/UrlParser.java

@@ -37,7 +37,10 @@ public static Map<String, String> parse(String url, String separator) {
     for (String keyValue : keyValues) {
       int separatorKey = keyValue.indexOf("="); // Find the first equal sign to split key and value.
       String key = keyValue.substring(0, separatorKey);
-      String value = keyValue.substring(separatorKey + 1);
+      String value = "";
+      if (!keyValue.endsWith("=")) { // Avoid crashes for empty values.
+        value = keyValue.substring(separatorKey + 1);
+      }
       resultMap.put(key, value);
     }