combine different arrows and colorized background-shapes of the arrows

Question

This works:

@startuml
() a
() b
() c
() d
a 0--0 b
'c }|--|| d
@enduml

This works:

@startuml
() a
() b
() c
() d
'a 0--0 b
c }|--|| d
@enduml

This do not work:

@startuml
() a
() b
() c
() d
a 0--0 b
c }|--|| d
@enduml

1) Why?

2) There are any way to make the minimal cardinality 'zero' (ERD) in the arrow with white background instead of transparent? Example:

@startuml
entity a{
  attrib datatype
}

entity b{
  attrib datatype
}

a }o--o{ b
@enduml

(The line cut the circle that rapresents the minimal cardinality 'zero')

Answer 1

Hello F.,

Here is an answer only for the first point.

In fact:

A/ is a Component/Deployment diagram:

@startuml () a () b () c () d a 0--0 b 'c }|--|| d @enduml	@startuml node n () a () b () c () d a 0--0 b 'c }|--|| d @enduml

B/ is a Class diagram:

@startuml () a () b () c () d 'a 0--0 b c }|--|| d @enduml	@startuml class C () a () b () c () d 'a 0--0 b c }|--|| d @enduml

That is the reason that the two arrow type can not to be mix...
(between Component/Deployment diagram and Class diagram!)

And even with the 'allow_mixing' parameter, we observed the error:

@startuml allow_mixing class C node n () a () b () c () d 'a 0--0 b c }|--|| d @enduml	@startuml allow_mixing class C node n () a () b () c () d a 0--0 b c }|--|| d @enduml

If that can help,
Regards,
Th.