Error: "Can not create JDBC driver of class '' for connect URL 'null' java.sql.SQLException: No suitable driver"

Hello, I'm trying to set up the connection to the database in my JPA application using JNDI. I'm following this tutorial ( link ), but even so when I try to make any query the system gives error saying it did not find the driver of the bank. I'm using the Tomcat 8, Eclipse, and Postgres SQL 9.1 container.

I made the following settings:

1- Tomcat's lib directory where I put the driver:

2-Application-specificcontext.xmlfile:

<?xmlversion="1.0" encoding="UTF-8"?>
<Context>
<WatchedResource>WEB-INF/web.xml</WatchedResource>
<WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
<!-- Deixa a conexão com o banco a cargo do container -->
<Resource name="jdbc/gymclub" auth="Container" type="javax.sql.DataSource"
           maxActive="100" maxIdle="30" maxWait="10000"
           username="admin" password="123456" driverclassname="org.postgresql.Driver"
           url="jdbc:postgresql://localhost:5432/gymclub"/>
</Context>

3- web.xml:

<resource-ref>
 <description>postgreSQL Datasource example</description>
 <res-ref-name>jdbc/gymclub</res-ref-name>
 <res-type>javax.sql.DataSource</res-type>
 <res-auth>Container</res-auth>
</resource-ref>

4- persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
xmlns="http://xmlns.jcp.org/xml/ns/persistence"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="gymclub">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <!-- Deixa o controle de conexão com o banco a cargo do container. -->
    <non-jta-data-source>java:/comp/env/jdbc/gymclub</non-jta-data-source>
    <!-- Habilita cache de segundo nivel <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode> -->
    <properties>
        <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL9Dialect" />
        <!-- False no ambiente de produção -->
        <property name="hibernate.show_sql" value="true" />
        <property name="hibernate.format_sql" value="true" />
        <!-- None no ambiente de produção -->
        <property name="hibernate.hbm2ddl.auto" value="update" />
        <!-- Essa propriedade permite que as sequences sejam criadas com os valores 
            iniciais que são especificados no domínio. -->
        <property name="hibernate.id.new_generator_mappings" value="true" />
        <!-- Cache de segundo nivel do hibernate <property name="hibernate.cache.region.factory_class" 
            value="org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory" /> -->
    </properties>
</persistence-unit>

When I run the application, tomcat throws the following exception:

Cannot create JDBC driver of class '' for connect URL 'null'
java.sql.SQLException: No suitable driver
at java.sql.DriverManager.getDriver(DriverManager.java:315)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createConnectionFactory(BasicDataSource.java:2144)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createDataSource(BasicDataSource.java:2032)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1532)
at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:139)
at org.hibernate.engine.jdbc.internal.JdbcServicesImpl$ConnectionProviderJdbcConnectionAccess.obtainConnection(JdbcServicesImpl.java:279)
at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:124)
at org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:111)
at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:234)
at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:206)
at org.hibernate.cfg.Configuration.buildTypeRegistrations(Configuration.java:1887)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1845)
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:852)
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:845)
at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.withTccl(ClassLoaderServiceImpl.java:398)
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:844)
at org.hibernate.jpa.HibernatePersistenceProvider.createEntityManagerFactory(HibernatePersistenceProvider.java:75)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:54)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:55)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:39)

Does anyone know how to solve it? I've already searched in several places and found no solution = /