Fix NPE with RepositoryHasDependency as precondition

[greg-at-moderne]

What's changed?

Add a guard against NPE (NullPointerException) for when RepositoryHasDependency is used as a precondition.

What's your motivation?

Address NPEs observed in the Moderne product against some repositories:

java.lang.NullPointerException: Cannot invoke "java.util.concurrent.atomic.AtomicBoolean.get()" because "acc" is null
  org.openrewrite.java.dependencies.search.RepositoryHasDependency.getVisitor(RepositoryHasDependency.java:100)
  org.openrewrite.java.dependencies.search.RepositoryHasDependency.getVisitor(RepositoryHasDependency.java:28)
  org.openrewrite.config.DeclarativeRecipe.orVisitors(DeclarativeRecipe.java:517)
  org.openrewrite.config.DeclarativeRecipe.lambda$getRecipeList$1(DeclarativeRecipe.java:500)
  org.openrewrite.Preconditions.lambda$and$0(Preconditions.java:111)
  org.openrewrite.config.DeclarativeRecipe$PreconditionBellwether$1.<init>(DeclarativeRecipe.java:233)
  org.openrewrite.config.DeclarativeRecipe$PreconditionBellwether.getVisitor(DeclarativeRecipe.java:232)
  org.openrewrite.config.DeclarativeRecipe$BellwetherDecoratedRecipe.getVisitor(DeclarativeRecipe.java:284)
  org.openrewrite.config.DeclarativeRecipe$BellwetherDecoratedRecipe.getVisitor(DeclarativeRecipe.java:284)
  org.openrewrite.config.DeclarativeRecipe$BellwetherDecoratedRecipe.getVisitor(DeclarativeRecipe.java:284)
  org.openrewrite.scheduling.RecipeRunCycle.lambda$editSource$10(RecipeRunCycle.java:223)
  org.openrewrite.scheduling.RecipeStack.reduce(RecipeStack.java:60)
  org.openrewrite.scheduling.RecipeRunCycle.editSource(RecipeRunCycle.java:200)
  org.openrewrite.scheduling.RecipeRunCycle.lambda$editSources$8(RecipeRunCycle.java:194)
  io.moderne.worker.execution.CountingModerneLargeSourceSet.lambda$edit$4(CountingModerneLargeSourceSet.java:132)
  io.moderne.serialization.ModerneLargeSourceSet.edit(ModerneLargeSourceSet.java:450)
  ...

Considerations

I am not fully sure if this is enough. Maybe we should investigate the upstream, i.e. main OpenRewrite, whether it should be like this.

[sambsnyd]

false is already the default value for AtomicBoolean, I don't see how this could make any difference at all.

[timtebeek]

Restored in cd273ba