If user forgets to fill mandatory property but IDEA does not show any warning message about it and in deployment phase Application server, e.g. Tomcat, can raise an exception like this: SEVERE: Servlet.service() for servlet jsp threw exception javax.servlet.jsp.JspException: You must specify exactly one of src, srcKey, page, or pageKey at org.apache.struts.taglib.html.ImageTag.src(ImageTag.java:264) at org.apache.struts.taglib.html.ImageTag.prepareButtonAttributes(ImageTag.java:157) at org.apache.struts.taglib.html.SubmitTag.doEndTag(SubmitTag.java:158) at org.apache.jsp.Struts.struts_jsp._jspx_meth_html_image_0(org.apache.jsp.Struts.struts_jsp:187) at org.apache.jsp.Struts.struts_jsp._jspx_meth_html_form_0(org.apache.jsp.Struts.struts_jsp:117) at org.apache.jsp.Struts.struts_jsp._jspService(org.apache.jsp.Struts.struts_jsp:78) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97) at javax.servlet.http.HttpServlet.service(HttpServlet.java:802) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264) at javax.servlet.http.HttpServlet.service(HttpServlet.java:802) ....