Fix test

Author: odersky

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -249,6 +249,7 @@ class CompilationTests {
       compileFilesInDir("tests/explicit-nulls/pos-patmat", explicitNullsOptions and "-Xfatal-warnings"),
       compileFilesInDir("tests/explicit-nulls/unsafe-common", explicitNullsOptions and "-language:unsafeNulls"),
       compileFile("tests/explicit-nulls/pos-special/i14682.scala", explicitNullsOptions and "-Ysafe-init"),
+      compileFile("tests/explicit-nulls/pos-special/i14947.scala", explicitNullsOptions and "-Ytest-pickler" and "-Xprint-types"),
     )
   }.checkCompile()