Spring cant convert String to Date on Server, local tests pass

[Alex04]

Hello,
I do have some controllers reading the conditional get header form an request.
In detail the "If-Modified-Since" header is required.
My Unit tests looks as follows:

// setup date
		Date currentDate = mu2.getLastModified();
		Calendar calendar = Calendar.getInstance();
		calendar.setTime(currentDate);
		calendar.add(Calendar.DATE, 1);
		//Sat, 12 Aug 1995 13:30:00 GMT+0000
		//EEE, dd.MM.yyyy HH:mm:ss Z
		SimpleDateFormat formatter = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zZ");
		formatter.setTimeZone((TimeZone.getTimeZone("GMT")));
		
		// setup request
		request.setMethod("GET");
		request.setRequestURI("/customer");
		request.addHeader("Accept", "application/json");
		request.addHeader("If-Modified-Since", formatter.format((calendar.getTime())));

So local all tests are fine and pass. On the Jenkins I'll get an Exception:

org.springframework.beans.ConversionNotSupportedEx ception: Failed to convert value of type 'java.lang.String' to required type 'java.util.Date'; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [java.util.Date]: no matching editors or conversion strategy found

How is that possible?

Local everything allright, on the jenkins thos errors?

I would appreciate any help