fix #853 - repair classloader for spring

Author: kamilkrzywanski

querydsl-tooling/querydsl-codegen-utils/src/main/java/com/querydsl/codegen/utils/JDKEvaluatorFactory.java

@@ -18,10 +18,7 @@
 import java.io.IOException;
 import java.io.StringWriter;
 import java.io.Writer;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 import javax.tools.JavaCompiler;
 import javax.tools.SimpleJavaFileObject;
 import javax.tools.StandardLocation;
@@ -50,7 +47,8 @@ public JDKEvaluatorFactory(ClassLoader parent, JavaCompiler compiler) {
     this.fileManager =
         new MemFileManager(parent, compiler.getStandardFileManager(null, null, null));
     this.compiler = compiler;
-    this.classpath = SimpleCompiler.getClassPath(parent);
+    this.classpath = Optional.of(SimpleCompiler.getClassPath(parent)).filter(s -> !s.isEmpty())
+            .orElseGet(() -> SimpleCompiler.getClassPath(compiler.getClass().getClassLoader()));
     this.loader = fileManager.getClassLoader(StandardLocation.CLASS_OUTPUT);
     this.compilationOptions = Arrays.asList("-classpath", classpath, "-g:none");
   }