Variable declaratino missing wenn miltiple operations are used

Hi,
ich tried to create a query based on GraphQLMultiQueryRequest using variable references:

quey ($request1: Type1m $request2: Type2){
op1(request: $request1){
...
}
op2 (request: $request2){
...
}
}

by setting up variable references in the first request I am using in the GraphQLMultiQueryRequest for serializtion.
The query, that I get from call of the method serialize ist
quey{
op1(request: $request1){
...
}
op2 (request: $request2){
...
}
}
which cannot be performed, as the engine cannot have an idea of the type of operations the arguments.
I figured, that it might be, that just

operationDef.variableDefinitions(variableDefinitions)...
is missing in the implementation of GraphQLMultiQueryRequest. However, as I can see, that variableDefinitions are collected earlier in the code, there might be a reason I'm unaware off, that is prohibiting to do so.
Please let me know, whether or not the code change I'm suggesting will work and if not, what would be the right way to deal with such a situation.

Start at GraphQLMultiQueryRequest serialization, focusing on how variable definitions are collected and passed to the operation definition. Reproduce the two-operation query from the issue and verify that serialization retains the variable declarations so the resulting query can be executed.