There is an important art theory that assumes that artists express their emotions through their art, so art is here considered as a form of self-expression by the artist.
That is one main element of this theory. There is a second element however. The perceiver will appreciate a work of art because it affects him or her in one way or the other, it generates emotions with the perceiver, positively or negatively.
I am inclined to extend that latter aspect. If it is true that real art leaves space for the perceiver to ‘complete it’, using his imagination, then emotions will play a role. Hence, also the perceiver will express emotions in his understanding and interpretation of the work of art, and in this way make it complete.