Remove only existance of 'null' from documentation (#2348)

Author: sazzad16

src/main/java/redis/clients/jedis/Jedis.java

@@ -191,8 +191,9 @@ public String set(final String key, final String value, final SetParams params)
   }
 
   /**
-   * Get the value of the specified key. If the key does not exist null is returned. If the value
-   * stored at key is not a string an error is returned because GET can only handle string values.
+   * Get the value of the specified key. If the key does not exist the special value 'nil' is
+   * returned. If the value stored at key is not a string an error is returned because GET can only
+   * handle string values.
    * <p>
    * Time complexity: O(1)
    * @param key