[JENKINS-43507] re-use Throwable.getMessage()

src/main/java/org/jenkinsci/plugins/github_branch_source/FillErrorResponse.java

@@ -13,11 +13,10 @@
// TODO replace with corresponding core functionality once Jenkins core has JENKINS-42443
class FillErrorResponse extends IOException implements HttpResponse {

    private final String message;
    private final boolean clearList;

    public FillErrorResponse(String message, boolean clearList) {
        this.message = message;
        super(message);
        this.clearList = clearList;
    }

@@ -29,7 +28,7 @@ public void generateResponse(StaplerRequest req, StaplerResponse rsp, Object nod
        rsp.setHeader("X-Jenkins-Select-Error", clearList ? "clear" : "retain");
        rsp.getWriter().print(
                "<div class=\'error\'><img src=\'" + req.getContextPath()
                        + Jenkins.RESOURCE_PATH + "/images/none.gif\' height=16 width=1>" + Util.escape(message) +
                        + Jenkins.RESOURCE_PATH + "/images/none.gif\' height=16 width=1>" + Util.escape(getMessage()) +
                        "</div>");

    }