Google Cloud Endpoints Framework 2 (Java) Error Meaning and Origin?

Question

Migrating to Framework 2. Using Java 8. What is the below error message trying to tell me? What might be wrong with my class annotations or web.xml? I am using Servlets 3.1.0 for other servlets. Does this enter into the equation?

com.google.apphosting.runtime.jetty9.JettyLogger warn: 
    Error for /_ah/api/taxdochubapi/v1/taxdoc/retrievewithguid
    (JettyLogger.java:29)

java.lang.NoClassDefFoundError:
    com/google/appengine/repackaged/com/google/common/base/Function
    at com.google.api.server.spi.EndpointsServlet.init(EndpointsServlet.java:56)
    at org.eclipse.jetty.servlet.ServletHolder.initServlet(ServletHolder.java:643)
    at org.eclipse.jetty.servlet.ServletHolder.getServlet(ServletHolder.java:499)
    ...

// Relevant annotation
@ApiMethod( name = "taxdocument.retrieve.withguid", 
            path = "taxdoc/retrievewithguid", 
            httpMethod = HttpMethod.GET )
public Map<String, String> retrieveTaxDocForGuid( @Named("guid") String guid ) {

<!-- web.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1">
    <servlet>
         <servlet-name>EndpointsServlet</servlet-name>
         <servlet-class>com.google.api.server.spi.EndpointsServlet</servlet-class>
         <init-param>
             <param-name>services</param-name>
             <param-value>com.taxdochub.endpoints.spi.TaxDocHubApiDocuments</param-value>
         </init-param>
         <init-param>
             <param-name>restricted</param-name>
             <param-value>false</param-value>
         </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>EndpointsServlet</servlet-name>
        <url-pattern>/_ah/api/*</url-pattern>
    </servlet-mapping>
    <welcome-file-list>
         <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

Answer 1

The problem was caused by my leaving a v1 dependency in my pom.xml file. After removing the below dependency, it started working.

    <dependency>
        <groupId>com.google.appengine</groupId>
        <artifactId>appengine-endpoints</artifactId>
        <version>${appengineVersion}</version>
    </dependency>