### Question:
StripeTextUtils { @Nullable public static String nullIfBlank(@Nullable String value) { if (isBlank(value)) { return null; } return value; }  @Nullable static String nullIfBlank(@Nullable String value); static boolean isBlank(@Nullable String value); @Nullable static String removeSpacesAndHyphens(@Nullable String cardNumberWithSpaces);  }### Answer:
@Test public void testNullIfBlankNullShouldBeNull() { assertEquals(null, StripeTextUtils.nullIfBlank(null)); }
@Test public void testNullIfBlankEmptyShouldBeNull() { assertEquals(null, StripeTextUtils.nullIfBlank("")); }
@Test public void testNullIfBlankSpaceShouldBeNull() { assertEquals(null, StripeTextUtils.nullIfBlank(" ")); }
@Test public void testNullIfBlankSpacesShouldBeNull() { assertEquals(null, StripeTextUtils.nullIfBlank(" ")); }
@Test public void testNullIfBlankTabShouldBeNull() { assertEquals(null, StripeTextUtils.nullIfBlank(" ")); }
@Test public void testNullIfBlankNumbersShouldNotBeNull() { assertEquals("0", StripeTextUtils.nullIfBlank("0")); }
@Test public void testNullIfBlankLettersShouldNotBeNull() { assertEquals("abc", StripeTextUtils.nullIfBlank("abc")); }