java.lang.IllegalStateException: Failed to execute CommandLineRunner (java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke)

Question

Hi I am very new to Spring, i was trying to execute this code using jpa, postgres and mapstruct:

package com.fundamentos.springboot.fundamentos;

import com.fundamentos.springboot.fundamentos.PERSISTENCE.ProductoRepo;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class FundamentosApplication implements CommandLineRunner {
    ProductoRepo productoRepo;
    public static void main(String[] args) {
        SpringApplication.run(FundamentosApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {



        productoRepo.getByCategory(1);
    }
}

and I am getting the following exception which I am not able to resolve when i try to execute the productoRepo.getByCategory(1); method:

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:780) ~[spring-boot-2.6.4.jar:2.6.4]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:761) ~[spring-boot-2.6.4.jar:2.6.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:310) ~[spring-boot-2.6.4.jar:2.6.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) ~[spring-boot-2.6.4.jar:2.6.4]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) ~[spring-boot-2.6.4.jar:2.6.4]
    at com.fundamentos.springboot.fundamentos.FundamentosApplication.main(FundamentosApplication.java:13) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.6.4.jar:2.6.4]
Caused by: java.lang.NullPointerException: null
    at com.fundamentos.springboot.fundamentos.FundamentosApplication.run(FundamentosApplication.java:21) ~[classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:777) ~[spring-boot-2.6.4.jar:2.6.4]
    ... 10 common frames omitted

2022-03-18 14:48:29.320  INFO 7664 --- [  restartedMain] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'default'
2022-03-18 14:48:29.652  INFO 7664 --- [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-03-18 14:48:29.809  INFO 7664 --- [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.
Disconnected from the target VM, address: '127.0.0.1:56906', transport: 'socket'

Process finished with exit code 0

I am not passing any commandline arguments and this exception doesn't occur all the time.

pomxl:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.fundamentos.springboot</groupId>
    <artifactId>fundamentos</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>fundamentos</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
            <org.mapstruct.version>1.4.2.Final</org.mapstruct.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-jpa -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.postgresql/postgresql -->
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.3.3</version>
        </dependency>
            <dependency>
                <groupId>org.mapstruct</groupId>
                <artifactId>mapstruct</artifactId>
                <version>${org.mapstruct.version}</version>
            </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${project.parent.version}</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source> <!-- depending on your project -->
                    <target>1.8</target> <!-- depending on your project -->
                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>${org.mapstruct.version}</version>
                        </path>
                        <!-- other annotation processors -->
                    </annotationProcessorPaths>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>