Rascal：createM3FromEclipseProject处的NullPointerException

如何解决Rascal：createM3FromEclipseProject处的NullPointerException

以下带有Rascal的代码将不起作用：

module Exercise1

import IO;
import IO;
import lang::java::jdt::m3::Core;

public void testing()
{
M3 model = createM3FromEclipseProject(|project://JabberPoint/|);
for (<a,b> <- model.extends)
println("<a> extends <b>");
}

结果为：

|plugin://Rascal_eclipse/src/org/Rascalmpl/eclipse/library/lang/java/jdt/m3/Core.rsc|(392,187,<13,0>,<15,90>): Java("NullPointerException","")
        at org.eclipse.jdt.core.dom.compilationunitResolver.resolve(|unkNown:///compilationunitResolver.java|(0,<599,0>))
        at org.eclipse.jdt.core.dom.ASTParser.createASTs(|unkNown:///ASTParser.java|(0,<906,0>))
        at org.Rascalmpl.eclipse.library.lang.java.jdt.m3.internal.EclipseJavaCompiler.compileAllFiles(|unkNown:///EclipseJavaCompiler.java|(0,<88,0>))....

可能是什么问题？ 谢谢。