Add nullability check for cache file

Author: sfc-gh-pbulawa

src/main/java/net/snowflake/client/core/FileCacheManager.java

@@ -264,7 +264,7 @@ synchronized <T> T withLock(Supplier<T> supplier) {
   /** Reads the cache file. */
   synchronized JsonNode readCacheFile() {
     try {
-      if (!cacheFile.exists()) {
+      if (cacheFile == null || !cacheFile.exists()) {
         logger.debug("Cache file doesn't exists. File: {}", cacheFile);
         return null;
       }

src/test/java/net/snowflake/client/core/FileCacheManagerTest.java

@@ -107,6 +107,26 @@ public void throwWhenReadCacheFileWithPermissionDifferentThanReadWriteForUserTes
     }
   }
 
+  @Test
+  @RunOnLinuxOrMac
+  public void notThrowExceptionWhenCacheFolderIsNotAccessible() throws IOException {
+    try {
+      Files.setPosixFilePermissions(
+          cacheFile.getParentFile().toPath(), PosixFilePermissions.fromString("---------"));
+      FileCacheManager fcm =
+          FileCacheManager.builder()
+              .setCacheDirectorySystemProperty(CACHE_DIR_PROP)
+              .setCacheDirectoryEnvironmentVariable(CACHE_DIR_ENV)
+              .setBaseCacheFileName(CACHE_FILE_NAME)
+              .setCacheFileLockExpirationInSeconds(CACHE_FILE_LOCK_EXPIRATION_IN_SECONDS)
+              .build();
+      assertDoesNotThrow(fcm::readCacheFile);
+    } finally {
+      Files.setPosixFilePermissions(
+          cacheFile.getParentFile().toPath(), PosixFilePermissions.fromString("rwx------"));
+    }
+  }
+
   @Test
   @RunOnLinuxOrMac
   public void throwWhenOverrideCacheFileHasDifferentOwnerThanCurrentUserTest() {