obscure message from resolver

[Jonathan Gibbons]

How do I read this message:

org.openjdk.jigsaw.ConfigurationException: Main@=1.0: Cannot resolve
    at org.openjdk.jigsaw.Resolver.fail(Resolver.java:81)

Is it
a) somewhere in Main@=1.0 (where did the '=' come from) there is 
something unspecified it cannot resolve
b) it cannot resolve a reference (where?) to Main@=1.0


I have a module Main at 1.0 (no '=') that just has a "requires M1;" (no 
version).  javac has auto-inserted a "requires synthetic jdk@=7-ea;".  
I'm compiling Main.  M1 is installed in the module library.

-- Jon