Sessions could not be save for empty workspaces since...

Sessions could not be save for empty workspaces since LoadSaveFunctions.SaveToConn expected a non-empty list of variables to store. However, GnuR allows to do so.
Also fixed problem when using function "q()" in test cases which caused the test suite to crash due to an unexpected but legitimate exception.

com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/LoadSaveFunctions.java

@@ -196,7 +196,7 @@ public class LoadSaveFunctions {
 
         @Override
         protected void createCasts(CastBuilder casts) {
-            casts.arg("list").mustBe(stringValue()).asStringVector().mustBe(notEmpty(), RError.Message.FIRST_ARGUMENT_NOT_CHARVEC).findFirst();
+            casts.arg("list").mustBe(stringValue()).asStringVector();
             ConnectionFunctions.Casts.connection(casts);
             casts.arg("ascii").mustBe(logicalValue(), RError.Message.ASCII_NOT_LOGICAL);
             casts.arg("version").allowNull().mustBe(integerValue());

com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

@@ -41706,6 +41706,9 @@ $ix
  [1] -Inf -Inf -Inf -Inf -Inf -Inf    0    1    2    3    4    5  Inf  Inf  Inf
 [16]  Inf  Inf
+##com.oracle.truffle.r.test.builtins.TestBuiltin_quit.testQuitEmptyEnv#
+#{ quit("yes") }
+
 ##com.oracle.truffle.r.test.builtins.TestBuiltin_quit.testQuitErrorSave#
 #{ quit("xx") }
 Error in quit(save, status, runLast) : unrecognized value of 'save'

com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/builtins/TestBuiltin_quit.java

 /*
- * Copyright (c) 2016, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -32,4 +32,9 @@ public class TestBuiltin_quit extends TestBase {
     public void testQuitErrorSave() {
         assertEval("{ quit(\"xx\") }");
     }
+
+    @Test
+    public void testQuitEmptyEnv() {
+        assertEval("{ quit(\"yes\") }");
+    }
 }

com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/generate/FastRSession.java

@@ -35,6 +35,7 @@ import com.oracle.truffle.api.debug.SuspendedCallback;
 import com.oracle.truffle.api.debug.SuspendedEvent;
 import com.oracle.truffle.api.source.Source;
 import com.oracle.truffle.api.vm.PolyglotEngine;
+import com.oracle.truffle.r.runtime.ExitException;
 import com.oracle.truffle.r.runtime.RCmdOptions;
 import com.oracle.truffle.r.runtime.RCmdOptions.Client;
 import com.oracle.truffle.r.runtime.RError;
@@ -234,6 +235,8 @@ public final class FastRSession implements RSession {
             }
         } catch (ParseException e) {
             e.report(consoleHandler);
+        } catch (ExitException e) {
+            // exit exceptions are legitimate if a test case calls "q()"
         } catch (RError e) {
             // nothing to do
         } catch (Throwable t) {