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This is called barrel distortion. This kind of distortion a natural property of any lens, from basic to ultra-professional. Obviously, lens designers strive to reduce it, but it is impossible to eliminate it in zoom lens for the entire range of focal lengths. The strength (and direction) of the effect typically depends on the current focal length setting of the lens.
Distortions like that are typically corrected in post-processing, e.g. in software.