code: private String determineQualifiedName(String name, CompilationUnit from) {
          if (from != null) {
              // Determine qualified name as being relative to "from"
  
              String fromName = from.getName();
              int index = fromName.lastIndexOf('.');
              if (index >= 0) {
                  String qual = fromName.substring(0, index + 1) + name;
                  if (sourceExists(qual)) {
                      return qual;
                  }
              }
          }
  
          if (sourceExists(name)) {
              return name;
          }
  
          return null;
      }
docs: Given a name, as requested by the given CompilationUnit, return a
  fully qualified name or null if the name could not be found.
  
  @param name requested name
  @param from optional CompilationUnit