Check null to avoid null pointer exception

Check if the string input is null in `getFirstLicenseToken` and `isSingleTokenString`

Signed-off-by: Arthit Suriyawongkul <arthit@gmail.com>

Author: bact

src/main/java/org/spdx/utility/compare/LicenseCompareHelper.java

@@ -190,12 +190,25 @@ public static String locateOriginalText(String fullLicenseText, int startToken,
         }
         // ignore
     }
-	
-	/*
-	 * @param text text to test
-	 * @return the first token in the license text
+
+	/**
+	 * Return the first license token found in the given text
+	 * <p>
+	 * The method normalizes the input text, removes comment characters,
+	 * and splits it into tokens
+	 * using {@link LicenseTextHelper#TOKEN_SPLIT_PATTERN}.
+	 * It returns the first non-empty token found,
+	 * or {@code null} if no such token exists.
+	 * </p>
+	 *
+	 * @param text The license text to extract the first token from.
+	 * @return The first non-empty token as a {@link String},
+	 *         or {@code null} if none is found.
 	 */
 	public static String getFirstLicenseToken(String text) {
+		if (text == null) {
+			return null;
+		}
 		String textToTokenize = LicenseTextHelper.normalizeText(LicenseTextHelper.replaceMultWord(LicenseTextHelper.replaceSpaceComma(
 				LicenseTextHelper.removeLineSeparators(removeCommentChars(text))))).toLowerCase();
 		Matcher m = LicenseTextHelper.TOKEN_SPLIT_PATTERN.matcher(textToTokenize);
@@ -206,12 +219,23 @@ public static String getFirstLicenseToken(String text) {
 		}
 		return null;
 	}
-	
+
 	/**
-	 * @param text text to test
-	 * @return true if the text contains a single token
+	 * Check whether the given text contains only a single token
+	 * <p>
+	 * A single token string is defined as a non-null string that does not
+	 * contain any newline characters and contains exactly one non-empty token
+	 * as identified by the {@link LicenseTextHelper#TOKEN_SPLIT_PATTERN}.
+	 * </p>
+	 *
+	 * @param text The text to test.
+	 * @return {@code true} if the text contains a single token,
+	 *         {@code false} otherwise.
 	 */
 	public static boolean isSingleTokenString(String text) {
+		if (text == null) {
+			return false;
+		}
 		if (text.contains("\n")) {
 			return false;
 		}

src/test/java/org/spdx/utility/compare/LicenseCompareHelperTest.java

@@ -539,18 +539,19 @@ public void testLicenseEqualsNoneLicense() throws InvalidSPDXAnalysisException,
 		Map<String, String> xlationMap = new HashMap<>();;
 		assertTrue(LicenseCompareHelper.isLicenseEqual(lic3, lic4, xlationMap));
 		assertFalse(LicenseCompareHelper.isLicenseEqual(lic4, lic2, xlationMap));
-	}	
-	
-	
+	}
+
 	public void testisSingleTokenString() {
+		assertTrue(LicenseCompareHelper.isSingleTokenString(""));
 		assertTrue(LicenseCompareHelper.isSingleTokenString(" token "));
 		assertTrue(LicenseCompareHelper.isSingleTokenString("'"));
 		assertTrue(LicenseCompareHelper.isSingleTokenString(" '"));
 		assertTrue(LicenseCompareHelper.isSingleTokenString("' "));
 		assertFalse(LicenseCompareHelper.isSingleTokenString("a and"));
 		assertFalse(LicenseCompareHelper.isSingleTokenString("a\nand"));
+		assertFalse(LicenseCompareHelper.isSingleTokenString(null));
 	}
-	
+
 	public void regressionTestMatchingGpl20Only() throws IOException, InvalidSPDXAnalysisException, SpdxCompareException {
 		String compareText = UnitTestHelper.fileToText(GPL_2_TEXT);
 		DifferenceDescription result = LicenseCompareHelper.isTextStandardLicense(LicenseInfoFactory.getListedLicenseById("GPL-2.0-only"), compareText);
@@ -568,11 +569,16 @@ public void testMatchingStandardLicenseIds() throws IOException, InvalidSPDXAnal
 			assertTrue(result[3].startsWith("GPL-2"));
 		}
 	}
-	
+
 	public void testFirstLicenseToken() {
 		assertEquals("first", LicenseCompareHelper.getFirstLicenseToken("   first,token that is needed\nnext"));
+		assertEquals("first", LicenseCompareHelper.getFirstLicenseToken("// first,second"));
+		assertNull(LicenseCompareHelper.getFirstLicenseToken(null));
+		assertNull(LicenseCompareHelper.getFirstLicenseToken(""));
+		assertNull(LicenseCompareHelper.getFirstLicenseToken("  <!-- -->"));
+		assertNull(LicenseCompareHelper.getFirstLicenseToken("# "));
 	}
-	
+
 	@SuppressWarnings("unused")
 	private String stringCharToUnicode(String s, int location) {
 		return "\\u" + Integer.toHexString(s.charAt(location) | 0x10000).substring(1);