IssueTracker

From internal report, seeing errors like the following:

 error: reference to map is ambiguous
          .map(
          ^
  both method <ToValue#1>map(Function<Value,ToValue#1>) in DataSource and method <ToValue#2>map(Function1<? super Value,? extends ToValue#2>) in DataSource match
  where ToValue#1,Value,Key,ToValue#2 are type-variables:
    ToValue#1 extends Object declared in method <ToValue#1>map(Function<Value,ToValue#1>)
    Value extends Object declared in class DataSource
    Key extends Object declared in class DataSource
    ToValue#2 extends Object declared in method <ToValue#2>map(Function1<? super Value,? extends ToValue#2>)

map is ambiguous with lambda syntax, due to having the same lambda signature for both variants.

Note - can't make it an extension in this case, since it's open (for legacy reasons).