cannot find newInstance() symbol #32

I try to compile my NC_writer class with
Class<?> Netcdf_writer = InMemoryJavaCompiler.newInstance().compile("meteoread.NC_writer", sourceCode.toString());

but it is not possible because newInstance() symbol cannot be found. I can use just
Class<?> Netcdf_writer = InMemoryJavaCompiler.compile("meteoread.NC_writer", sourceCode.toString());

It works in NetBeans IDE but after I built the program and I run the .jar file I get NulPointerException error. How should I fix this problem? I use InMemoryJavaCompiler-1.2