Merge pull request #1766 from sbt/fix/1766

Lots of "No main class detected" warnings since 0.13.7

main/src/main/scala/sbt/Defaults.scala

@@ -676,7 +676,6 @@ object Defaults extends BuildCommon {
     sbt.SelectMainClass(None, classes)
   private def pickMainClassOrWarn(classes: Seq[String], logger: Logger): Option[String] = {
     classes match {
-      case Nil                           => logger.warn("No main class detected")
       case multiple if multiple.size > 1 => logger.warn("Multiple main classes detected.  Run 'show discoveredMainClasses' to see the list")
       case _                             =>
     }

notes/0.13.8/no-mainclass.markdown

@@ -0,0 +1,13 @@
+  [@cunei]: https://github.com/cunei
+  [@eed3si9n]: https://github.com/eed3si9n
+  [@gkossakowski]: https://github.com/gkossakowski
+  [@jsuereth]: https://github.com/jsuereth
+  [1766]: https://github.com/sbt/sbt/pull/1766
+
+### Fixes with compatibility implications
+
+### Improvements
+
+### Bug fixes
+
+- Removes "No main class detected" warning. [#1766][1766] by [@eed3si9n][@eed3si9n]