Q:

java.lang.IllegalArgumentException: [Assertion failed] - this argument is required; it must not be null

Here I am Facing following issue when getting all data from solr using spring data solr repository's findAll() method.
But I can able to indexing successfully by using this same code configuration. For this I am using save(entity) method.
java.lang.IllegalArgumentException: [Assertion failed] - this argument is required; it must not be null
at org.springframework.util.Assert.notNull(Assert.java:112)
at org.springframework.util.Assert.notNull(Assert.java:123)
at org.springframework.data.solr.core.convert.MappingSolrConverter$SolrPropertyValueProvider.readValue(MappingSolrConverter.java:331)
at org.springframework.data.solr.core.convert.MappingSolrConverter$SolrPropertyValueProvider.readCollection(MappingSolrConverter.java:471)
at org.springframework.data.solr.core.convert.MappingSolrConverter$SolrPropertyValueProvider.readValue(MappingSolrConverter.java:345)
at org.springframework.data.solr.core.convert.MappingSolrConverter$SolrPropertyValueProvider.readValue(MappingSolrConverter.java:322)
at org.springframework.data.solr.core.convert.MappingSolrConverter$SolrPropertyValueProvider.getPropertyValue(MappingSolrConverter.java:308)
at org.springframework.data.solr.core.convert.MappingSolrConverter.getValue(MappingSolrConverter.java:152)
at org.springframework.data.solr.core.convert.MappingSolrConverter$1.doWithPersistentProperty(MappingSolrConverter.java:139)
at org.springframework.data.solr.core.convert.MappingSolrConverter$1.doWithPersistentProperty(MappingSolrConverter.java:131)
at org.springframework.data.mapping.model.BasicPersistentEntity.doWithProperties(BasicPersistentEntity.java:294)
at org.springframework.data.solr.core.convert.MappingSolrConverter.read(MappingSolrConverter.java:131)
at org.springframework.data.solr.core.convert.MappingSolrConverter.read(MappingSolrConverter.java:118)
at org.springframework.data.solr.core.convert.MappingSolrConverter.read(MappingSolrConverter.java:93)
at org.springframework.data.solr.core.SolrTemplate.convertSolrDocumentListToBeans(SolrTemplate.java:466)
at org.springframework.data.solr.core.SolrTemplate.queryForObject(SolrTemplate.java:279)
at org.springframework.data.solr.repository.support.SimpleSolrRepository.findOne(SimpleSolrRepository.java:97)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:442)
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:427)
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:381)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
at $Proxy34.findOne(Unknown Source)
at com.spring.datasolr.service.UserServiceImpl.getList(UserServiceImpl.java:78)
at com.spring.datasolr.controller.UserController.getUserList(UserController.java:45)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

Repository Class
public interface UserRepository extends SolrCrudRepository<User, String> {

}

SolrServer spring Bean configuration
<!-- Configures HTTP Solr server -->
        <solr:solr-server id="solrServer" url="${solr.server.host}" />

        <!-- Configures Solr template -->
        <bean id="solrTemplate" class="org.springframework.data.solr.core.SolrTemplate">
            <constructor-arg index="0" ref="solrServer" />
        </bean>
        <solr:repositories base-package="com.spring.datasolr.repository"></solr:repositories>

Entity class
import org.apache.solr.client.solrj.beans.Field;
import org.springframework.data.solr.core.mapping.Indexed;

public class User {

    @org.springframework.data.annotation.Id
    @Field(value="id")
    private int id;

    @Field(value="uname")
    private String name;

    @Field(value="uemail")
    private String email;

    @Field(value="upassword")
    private String password;

    @Field(value="umessage")
    private String message;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getMessage() {
        return message;
    }
    public void setMessage(String message) {
        this.message = message;
    }
}

schema.xml
<field name="uid" type="string" indexed="true" stored="true" multiValued="true"/>
   <field name="uname" type="string" indexed="true" stored="true" multiValued="true"/>
   <field name="uemail" type="string" indexed="true" stored="true" multiValued="true"/>
   <field name="umessage" type="string" indexed="true" stored="true" multiValued="true"/>
   <field name="upassword" type="string" indexed="true" stored="true" multiValued="true"/>

A:

Mark the multiValued="true" to multiValued="false"

