Fix some varargs compiler warnings in libcore tests.

Test: atest [all of the changed tests]
Change-Id: I78509a800adc217b1abca289c6bde53f51590a1e
diff --git a/luni/src/test/java/libcore/java/lang/invoke/MethodHandleCombinersTest.java b/luni/src/test/java/libcore/java/lang/invoke/MethodHandleCombinersTest.java
index 5866ae4..a8cfa24 100644
--- a/luni/src/test/java/libcore/java/lang/invoke/MethodHandleCombinersTest.java
+++ b/luni/src/test/java/libcore/java/lang/invoke/MethodHandleCombinersTest.java
@@ -1214,7 +1214,7 @@
 
         Object ret = handle.invokeWithArguments(new Object[]{"a", "b", "c"});
         assertEquals(42, (int) ret);
-        ret = handle.invokeWithArguments(new String[]{"a", "b", "c"});
+        ret = handle.invokeWithArguments((Object[]) new String[]{"a", "b", "c"});
         assertEquals(42, (int) ret);
 
         // Also test the versions that take a List<?> instead of an array.
diff --git a/luni/src/test/java/libcore/java/lang/invoke/MethodTypeTest.java b/luni/src/test/java/libcore/java/lang/invoke/MethodTypeTest.java
index f833840..0c4d18b 100644
--- a/luni/src/test/java/libcore/java/lang/invoke/MethodTypeTest.java
+++ b/luni/src/test/java/libcore/java/lang/invoke/MethodTypeTest.java
@@ -96,7 +96,7 @@
         }
 
         try {
-            MethodType.methodType(int.class, String.class, null);
+            MethodType.methodType(int.class, String.class, (Class<?>) null);
             fail();
         } catch (NullPointerException expected) {
         }
@@ -334,7 +334,7 @@
         }
 
         try {
-            mt.insertParameterTypes(1, Arrays.asList(null));
+            mt.insertParameterTypes(1, Arrays.asList((Class<?>) null));
             fail();
         } catch (NullPointerException expected) {
         }
@@ -404,7 +404,7 @@
         }
 
         try {
-            mt.appendParameterTypes(Arrays.asList(null));
+            mt.appendParameterTypes(Arrays.asList((Class<?>) null));
             fail();
         } catch (NullPointerException expected) {
         }
diff --git a/luni/src/test/java/libcore/java/nio/file/DefaultFileSystemProvider2Test.java b/luni/src/test/java/libcore/java/nio/file/DefaultFileSystemProvider2Test.java
index 2916b03..42d0f05 100644
--- a/luni/src/test/java/libcore/java/nio/file/DefaultFileSystemProvider2Test.java
+++ b/luni/src/test/java/libcore/java/nio/file/DefaultFileSystemProvider2Test.java
@@ -600,7 +600,8 @@
         } catch (NullPointerException expected) {}
 
         try {
-            provider.newByteChannel(filesSetup.getTestPath(), new HashSet<>(), null);
+            provider.newByteChannel(filesSetup.getTestPath(), new HashSet<>(),
+                (FileAttribute<?>) null);
             fail();
         } catch (NullPointerException expected) {}
     }
diff --git a/luni/src/test/java/libcore/java/nio/file/DefaultSecureDirectoryStreamTest.java b/luni/src/test/java/libcore/java/nio/file/DefaultSecureDirectoryStreamTest.java
index 2c9c2cd..273ff8f 100644
--- a/luni/src/test/java/libcore/java/nio/file/DefaultSecureDirectoryStreamTest.java
+++ b/luni/src/test/java/libcore/java/nio/file/DefaultSecureDirectoryStreamTest.java
@@ -185,7 +185,7 @@
 
             // NPE
             try (DirectoryStream<Path> ds_path_dir1 =  ds_path_root.newDirectoryStream(path_root.
-                    relativize(path_f1), null)) {
+                    relativize(path_f1), (LinkOption) null)) {
                 fail();
             } catch (NullPointerException expected) {}
 
@@ -380,7 +380,7 @@
 
         try {
             ds_path_dir1.move(path_dir1, ds_path_dir1,
-                    Paths.get(path_root.getParent().toString(), null));
+                    Paths.get(path_root.getParent().toString(), (String) null));
             fail();
         } catch (NullPointerException expected) {}
 
@@ -498,7 +498,7 @@
         try (SecureDirectoryStream<Path> ds_path_root = (SecureDirectoryStream<Path>)
                 Files.newDirectoryStream(path_root)) {
             ds_path_root.getFileAttributeView(path_root.relativize(path_f1),
-                    BasicFileAttributeView.class, null);
+                    BasicFileAttributeView.class, (LinkOption) null);
             fail();
         } catch (NullPointerException expected) {}
     }
diff --git a/luni/src/test/java/libcore/java/nio/file/Files2Test.java b/luni/src/test/java/libcore/java/nio/file/Files2Test.java
index 436d3e3..a3357e3 100644
--- a/luni/src/test/java/libcore/java/nio/file/Files2Test.java
+++ b/luni/src/test/java/libcore/java/nio/file/Files2Test.java
@@ -1683,7 +1683,7 @@
         } catch (NullPointerException expected) {}
 
         try {
-            Files.createTempDirectory(filesSetup.getTestDirPath(), tmpDir, null);
+            Files.createTempDirectory(filesSetup.getTestDirPath(), tmpDir, (FileAttribute<?>) null);
             fail();
         } catch (NullPointerException expected) {}
     }
@@ -1710,7 +1710,7 @@
         assertEquals(attr.value(), Files.getAttribute(tmpDirPath, attr.name()));
 
         try {
-            Files.createTempDirectory(tmpDir, null);
+            Files.createTempDirectory(tmpDir, (FileAttribute<?>) null);
             fail();
         } catch (NullPointerException expected) {}
     }
@@ -1757,7 +1757,7 @@
 
         try {
             Files.createTempFile(filesSetup.getTestDirPath(), tmpFilePrefix, tmpFileSuffix,
-                    null);
+                (FileAttribute<?>) null);
             fail();
         } catch (NullPointerException expected) {}
     }
@@ -1796,7 +1796,7 @@
         assertEquals(attr.value(), Files.getAttribute(tmpFilePath, attr.name()));
 
         try {
-            Files.createTempFile(tmpFilePrefix, tmpFileSuffix, null);
+            Files.createTempFile(tmpFilePrefix, tmpFileSuffix, (FileAttribute<?>) null);
             fail();
         } catch (NullPointerException expected) {}
     }
diff --git a/luni/src/test/java/libcore/java/nio/file/LinuxPathTest.java b/luni/src/test/java/libcore/java/nio/file/LinuxPathTest.java
index e95f5bc..458804c 100644
--- a/luni/src/test/java/libcore/java/nio/file/LinuxPathTest.java
+++ b/luni/src/test/java/libcore/java/nio/file/LinuxPathTest.java
@@ -18,6 +18,7 @@
 
 import com.sun.nio.file.ExtendedWatchEventModifier;
 
+import java.nio.file.WatchEvent.Kind;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Rule;
@@ -454,7 +455,7 @@
         } catch (NullPointerException expected) {}
 
         try {
-            directory.register(watchService, null);
+            directory.register(watchService, (Kind<?>) null);
             fail();
         } catch (NullPointerException expected) {}
     }