[FATAL] : ASSERTION FAILED When trying to use CameraPublisher

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Hi,

I've been trying to publish camera topics and when publishing image and camera_info topics with image_transport::CameraPublisher, using

image_transport::CameraPublisher left_image_pub;

left_image_pub.publish(left_image,left_cam_info);

I get:

[FATAL] [1427371749.536180328]: ASSERTION FAILED
    file = /tmp/buildd/ros-hydro-image-transport-1.11.4-0precise-20150101-0635/src/camera_publisher.cpp
    line = 126
    cond = false
    message = 
[FATAL] [1427371749.536421266]: Call to publish() on an invalid image_transport::CameraPublisher
[FATAL] [1427371749.536482747]: 

Trace/breakpoint trap (core dumped)

I would be very grateful if anyone could help me, because I tryied a lot to search about this subject but with no success.