failing compile test

compile-test.js

var google = Packages.com.google;
var jscomp = google.javascript.jscomp;
var ImmutableList = google.common.collect.ImmutableList;

var compiler = new jscomp.Compiler();

// assemble compiler options
var options = new jscomp.CompilerOptions();
options.setCodingConvention(new jscomp.ClosureCodingConvention());

// set compilation level
jscomp.CompilationLevel.SIMPLE_OPTIMIZATIONS.setOptionsForCompilationLevel(options);

// assemble externs
var externs = ImmutableList.of(
    jscomp.JSSourceFile.fromCode("extern.js", "")
);

// assemble inputs
var inputs = ImmutableList.of(
    jscomp.JSSourceFile.fromCode("input.js", "alert('hello')")
);

// compile
var result = compiler.compile(externs, inputs, options);
var out = compiler.toSource();