don't crash when appending an array to StringBuilder

idea/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -1316,7 +1316,7 @@ public class ExpressionCodegen extends JetVisitor {
         }
         Type exprType = expressionType(expr);
         gen(expr, exprType);
-        invokeAppendMethod(exprType);
+        invokeAppendMethod(exprType.getSort() == Type.ARRAY ? JetTypeMapper.TYPE_OBJECT : exprType);
     }
 
     public void invokeAppendMethod(Type exprType) {

idea/tests/org/jetbrains/jet/codegen/NamespaceGenTest.java

@@ -481,4 +481,12 @@ public class NamespaceGenTest extends CodegenTestCase {
         final Method main = generateFunction();
         assertEquals(false, ((Boolean) main.invoke(null, true)).booleanValue());
     }
+
+    public void testAppendArrayToString() throws Exception {
+        loadText("fun foo(a: String, b: Array<String>) = a + b");
+        final Method main = generateFunction();
+        final String[] args = new String[] { "foo", "bar" };
+        //noinspection ImplicitArrayToString
+        assertEquals("s" + args.toString(), main.invoke(null, "s", args));
+    }
 }