Only default parameters of Java Request Samplers are stored

**chris.p** ([Bug 42867](https://bz.apache.org/bugzilla//show_bug.cgi?id=42867&redirect=false)):
I created a new JavaSamplerClient by extending AbstractJavaSamplerClient. The
method getDefaultParameters returns five parameters with default values.

Everything works fine, but when I add a new Parameter to the Java Request, it
disappears when selecting another element in the left tree and changing back to
the Java Request.

If the Java Request settings are still open when executing the Test Plan, the
additional Parameter is handed over to the Java Request correctly. The parameter
even is stored in the JMX file, but when the file is loaded again, it disappears
again.

OS: All