assertEquals works in selenium but not in JAVA

I made a testcase in selenium which repeats perfectly and then exported it to JAVA /JUnit4 / Webdriver :

  public void emailInvalid() throws Exception {
        driver.get(baseUrl + "/test/contacts.html");
        driver.findElement(By.name("companyName")).clear();
        driver.findElement(By.name("companyName")).sendKeys("testcomp");
        driver.findElement(By.name("phone")).clear();
        driver.findElement(By.name("phone")).sendKeys("45454545");
        driver.findElement(By.name("email")).clear();
        driver.findElement(By.name("email")).sendKeys("test.ee");
        driver.findElement(By.name("message")).clear();
        driver.findElement(By.name("message")).sendKeys("qwerty");
        driver.findElement(By.cssSelector("button.submit")).click();
        assertEquals("Not valid email.", driver.findElement(By.cssSelector("span.error.notValidEmail")).getText());
  }

But for some reason the test fails in JAVA because assertEquals can't get the text its looking for. It also says " org.junit.ComparisonFailure: expected:<[Not valid email]> but was:<[]> "