public static void close(InputStream is) {
        if (is != null) {
            try {
                is.close();
            } catch (IOException e) {
                LOGGER.warn("Error closing input stream.", e);
            }
        }
    }
Convenience method that closes the specified {@link InputStream InputStream}, logging any
{@link IOException IOException} that might occur. If the {@code InputStream}
argument is {@code null}, this method does nothing.  It returns quietly in all cases.

@param is the {@code InputStream} to close, logging any {@code IOException} that might occur.
lang/src/main/java/org/apache/shiro/lang/io/ResourceUtils.java