Java Programming

Using Java 1.8 and JUnit 1.5, am trying to read a sample csv file for standalone sudoku app through which I try to read the CSV file through a JUnit test.
pom.xml:

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.sudoku</groupId>
    <artifactId>sudoku</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.1.0</version>
            <scope>test</scope>
        </dependency>
   
        <dependency>
            <groupId>org.hamcrest</groupId>
            <artifactId>hamcrest-library</artifactId>
            <version>2.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

Project structure:

sudoku
│
├── sudoku.iml
├── src
│  ├── test
│  │  ├── resources
│  │  │  ├─  valid.csv
│  │  └────  invalid.csv
│  │  └── java
│  │     └── com
│  │         └── sudoku
│  │             └── SudokuTest.java
│  └── main
│     ├── resources
│     │   ├── valid.csv
│     │   └── invalid.csv
│     └── java
│         └── com
│             └── sudoku
│                 └── Sudoku.java
├── pom.xml

Sudoku.java:

package com.sudoku;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.Arrays;

public class Sudoku {

    public static final int SIZE = 9;

    private final int[][] board = new int[SIZE][SIZE];

    public boolean isValidRow() {
        for (int x = 0; x < SIZE; x++) {
            if (isValidBoard(board[x])) {
                System.out.println("Invalid row: " + Arrays.toString(board[x]));
                return false;
            }
        }
        return true;
    }


    public static boolean isValidBoard(int[] boardMatrix) {
    	return Arrays.stream(boardMatrix).sum() == 45;
    }


     public void loadCsvFile(String csvFile) throws Exception {
        URL resource = getClass().getClassLoader().getResource(csvFile);
        BufferedReader csvReader = new BufferedReader(new InputStreamReader(resource.openStream()));
        int x = 0;
        String row = null;
        while ((row = csvReader.readLine()) != null) {
            String[] rows = row.split(",");
            int y = 0;
            for (String singleRow : rows) {
                if (singleRow != null || !"".equals(singleRow)) {
                    int rowIntegerValue = 0;
                    try {
                        rowIntegerValue = Integer.parseInt(singleRow);
                    }
                    catch (NumberFormatException nfe) {
                        nfe.printStackTrace();
                    }
                    if (rowIntegerValue < 1 || rowIntegerValue > 9) {
                        throw new IllegalArgumentException(rowIntegerValue + " is invalid. Must be in between 1 - 9.");
                    }
                    board[x][y] = rowIntegerValue;
                    y++;
                }
            }
            x++;
        }
        csvReader.close();
    }
}

SudokuTest.java

package com.sudoku;

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertTrue;

public class SudokuTest {

    @Test
    public void isValidRow() throws Exception {
        Sudoku sudoku = new Sudoku();
        sudoku.loadCsvFile("valid.csv");
        System.out.println("hello " + sudoku.isValidRow());
        assertTrue(sudoku.isValidRow());
    }
}

valid.csv:

9,2,3,4,5,6,7,8,1
4,5,6,7,8,9,1,2,3
7,8,9,1,2,3,4,5,6
5,3,4,5,6,7,8,9,1
2,6,7,8,9,1,2,3,4
8,9,1,2,3,4,5,6,7
3,4,5,6,7,8,9,1,2
6,7,8,9,1,2,3,4,5
9,1,2,4,3,5,6,7,8

When I run the JUnit file manually in IntelliJ IDEA Ultimate Edition, I get the following exception:

java.lang.NumberFormatException: For input string: ""
	at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:68)
	at java.base/java.lang.Integer.parseInt(Integer.java:662)
	at java.base/java.lang.Integer.parseInt(Integer.java:770)
	at com.sudoku.Sudoku.loadCsvFile(Sudoku.java:150)
	at com.sudoku.SudokuTest.isValidRow(SudokuTest.java:15)

java.lang.IllegalArgumentException: 0 is invalid. Must be in between 1 - 9.
	at com.sudoku.Sudoku.loadCsvFile(Sudoku.java:156)
	at com.sudoku.SudokuTest.isValidRow(SudokuTest.java:15)

This is weird because when using the debugger, it iterates and does parse values - I don't see a single 0 or "" anywhere in my code?
Why does this break?
Is there a better way to rewrite this Sudoku.loadCsvFile()method?