assertFalse("Expanded command should not contain ${mimetype}", expandedCommand.contains("${mimetype}"));
    }

    @Test
    public void test_mimetype_variable_replacement_nullMimeType() {
        final String testCommand = "generate-thumbnail image ${url} ${outputFile} ${mimetype}";
        final String tempPath = "/tmp/test.gif";
        final String outputPath = "/tmp/thumbnail.png";