Explicitly allow logVarargs to take an array containing null objects.

This is already supported for log() calls which take @NullableDect Object
params and then pass them into logImpl (see
http://third_party/java_src/flogger/api/src/main/java/com/google/common/flogger/LogContext.java?rcl=289240473&l=896).

This is so a @FormatMethod which uses "@nullable Object... args" can pass the
args directly to logVarargs() without a static analysis test failing.

RELNOTES=Explicitly allow an array containing null objects in logVarargs().

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=291245533

api/src/main/java/com/google/common/flogger/LogContext.java

@@ -1246,7 +1246,7 @@ public final void log(String message, double p1, double p2) {
   }
 
   @Override
-  public final void logVarargs(String message, Object[] params) {
+  public final void logVarargs(String message, @NullableDecl Object[] params) {
     if (shouldLog()) {
       // Copy the varargs array (because we didn't create it and this is quite a rare case).
       logImpl(message, Arrays.copyOf(params, params.length));

api/src/main/java/com/google/common/flogger/LoggingApi.java

@@ -287,7 +287,7 @@ API withInjectedLogSite(
    * @param message the message template string containing a single argument placeholder.
    * @param varargs the non-null array of arguments to be formatted.
    */
-  void logVarargs(String message, Object[] varargs);
+  void logVarargs(String message, @NullableDecl Object[] varargs);
 
   /**
    * Terminal log statement when a message is not required. A {@code log} method must terminate all

api/src/test/java/com/google/common/flogger/LogContextTest.java

@@ -258,10 +258,10 @@ public void testExplicitVarargs() {
     FakeLoggerBackend backend = new FakeLoggerBackend();
     FluentLogger logger = new FluentLogger(backend);
 
-    Object[] args = new Object[] {"foo", "bar", "baz"};
+    Object[] args = new Object[] {"foo", null, "baz"};
     logger.atInfo().logVarargs("Any message ...", args);
 
-    backend.assertLastLogged().hasArguments("foo", "bar", "baz");
+    backend.assertLastLogged().hasArguments("foo", null, "baz");
     // Make sure we took a copy of the arguments rather than risk re-using them.
     assertThat(backend.getLoggedCount()).isEqualTo(1);
     assertThat(backend.getLogged(0).getArguments()).isNotSameInstanceAs(args);