Sequence diagram empty directive marked as incorrect mermaidJS

[MaxWinsemius]

I noticed when working on sequenceDiagrams, that the method of rendering does not match with the mermaid live renderer.

When using the following snippet:

sequenceDiagram
    node_a->>node_b: comment
    node_b->>node_a: 

(Note the space at the end of line 3)

I get the following render from the live renderer:

But an error if build using sphinx:

Now I do not know if this syntax is even supported on purpose by Mermaid, since I didn't find any examples of that either and if I remove the space on line 3 it also fails.