code: public @CheckForNull
      Obligation getObligationByType(ClassDescriptor classDescriptor) {
          try {
              return getObligationByType(BCELUtil.getObjectTypeInstance(classDescriptor.toDottedClassName()));
          } catch (ClassNotFoundException e) {
              Global.getAnalysisCache().getErrorLogger().reportMissingClass(e);
              return null;
          }
      }
docs: Look up an Obligation by type. This returns the first Obligation that is
  a supertype of the type given (meaning that the given type could be an
  instance of the returned Obligation).
  
  @param classDescriptor
  a ClassDescriptor naming a class type
  @return an Obligation that is a supertype of the given type, or null if
  there is no such Obligation