When is csc theta = 0?

Here is the graph for  y=csc(x)

You can see that y=0 is an asymptote   

https://www.desmos.com/calculator/llizj9irtz

If csc(θ) = a/b, then sin(θ)  =  b/a.

Since csc(θ) = 0, then csc(θ) = 0/1  --->   sin(θ)  =  1/0   (which is undefined)

So csc(θ) can't equal 0.