So if i put a test charge +q between the lines(empty space between 2
field lines) so pictorally it says that no force should act on it.
No, that's not correct. The space between field lines does not mean the field does not exist between the lines.
You need to realize that electric field lines are used to visualize and analyze electric fields and therefore should be considered as a pictorial tool as opposed to a physical entity. For example, one cannot think of the space between the field lines in the picture, which, for example, get farther and farther apart the further away we go from the point charge producing the field, to be “devoid” of an electric field.
Instead of thinking of the strength of the field at a specific point in terms of the individual, discrete field lines, think of the electric field as a continuum or smear that gets fainter and fainter the farther away from the source. In addition to getting a feeling of the strength of the field in a general area based on the density of the lines, the other benefit of the "lines" picture vs the continuum picture is the former also allows one to see the direction of the field based on the arrows shown on the lines. You wouldn't get that picture if the field were represented only by different shades of gray.
So the benefits of using discrete lines with arrows and varying density is a compromise for visualizing the field.
Hope this helps.