index: make git_index_new() work with a NULL path

src/index.c

@@ -259,7 +259,7 @@ int git_index_open(git_index **index_out, const char *index_path)
 {
 	git_index *index;
 
-	assert(index_out && index_path);
+	assert(index_out);
 
 	index = git__calloc(1, sizeof(git_index));
 	GITERR_CHECK_ALLOC(index);

tests-clar/index/inmemory.c

+#include "clar_libgit2.h"
+
+void test_index_inmemory__can_create_an_inmemory_index(void)
+{
+	git_index *index;
+
+	cl_git_pass(git_index_new(&index));
+	cl_assert_equal_i(0, git_index_entrycount(index));
+
+	git_index_free(index);
+}