Fixes NPE on no-save-then-load situation

amm/interp/src/main/scala/ammonite/interp/Interpreter.scala

@@ -743,4 +743,4 @@ object Interpreter{
     )
     (colors, printStream, errorPrintStream, printer)
   }
-}
+}

amm/repl/src/main/scala/ammonite/repl/ApiImpls.scala

@@ -41,6 +41,7 @@ class SessionApiImpl(eval: Evaluator) extends Session{
     eval.frames = childFrame(next.head) :: next
     out
   }
+
   def load(name: String = "") = {
     val next = if (name == "") eval.frames.tail else namedFrames(name)
     val out = SessionChanged.delta(eval.frames.head, next.head)
@@ -51,7 +52,6 @@ class SessionApiImpl(eval: Evaluator) extends Session{
   def delete(name: String) = {
     namedFrames.remove(name)
   }
-  save()
 }
 class ReplApiImpl(val interp: Interpreter,
                   width0: => Int,
@@ -142,4 +142,4 @@ class ReplApiImpl(val interp: Interpreter,
     }
   }
 
-}
+}

amm/repl/src/main/scala/ammonite/repl/Repl.scala

@@ -38,10 +38,6 @@ class Repl(input: InputStream,
     """
   }.mkString(newLine)
 
-
-
-
-
   val interp: Interpreter = new Interpreter(
     printer,
     storage,
@@ -61,14 +57,19 @@ class Repl(input: InputStream,
         history,
         new SessionApiImpl(i.eval),
         replArgs
-
       )
       Seq(("ammonite.repl.ReplBridge", "repl", replApi))
     },
     wd
   )
 
-
+  // Call `session.save` _after_ the interpreter is fully instantiated and
+  // imports are loaded. We only need to do this in `Repl` and not in
+  // `Interpreter`, as using sess.save or load inside scripts is sketchy and
+  // probably not something we can support
+  interp.bridges.collectFirst {
+    case ("ammonite.repl.ReplBridge", _, r: ReplAPI) => r
+  }.foreach(_.sess.save())
 
   val reader = new InputStreamReader(input)
 
@@ -157,4 +158,4 @@ object Repl{
     )
     traces.mkString(newLine)
   }
-}
+}