Add docs

apps/opik-backend/src/main/java/com/comet/opik/utils/ValidationUtils.java

@@ -7,6 +7,24 @@
 
 public class ValidationUtils {
 
+    /**
+     * Regular expression to validate if a string is null or not blank.
+     *
+     * <p>It matches any string that is not null and contains at least one non-whitespace character.</p>
+     * For example:
+     * <ul>
+     *     <li>"" -> false</li>
+     *     <li>" " -> false</li>
+     *     <li>"\n" -> false</li>
+     *     <li>null -> true</li>
+     *     <li>"a" -> true</li>
+     *     <li>" a " -> true</li>
+     *     <li>"\n a \n" -> true</li>
+     * </ul>
+     *
+     * @see <a href="https://regexper.com/">Visual Explainer</a>
+     * @see <a href="https://zzzcode.ai/regex/explain">Ai Explainer</a>
+     */
     public static final String NULL_OR_NOT_BLANK = "(?s)^\\s*(\\S.*\\S|\\S)\\s*$";
 
     /**

apps/opik-backend/src/test/java/com/comet/opik/utils/ValidationUtilsTest.java

@@ -0,0 +1,30 @@
+package com.comet.opik.utils;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class ValidationUtilsTest {
+
+    public static Stream<Arguments> testNullOrNotBlank() {
+        return Stream.of(
+                Arguments.of("", false),
+                Arguments.of(" ", false),
+                Arguments.of("\n", false),
+                Arguments.of("a", true),
+                Arguments.of(" a ", true),
+                Arguments.of("\n a \n", true)
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource
+    void testNullOrNotBlank(String input, boolean expected) {
+        assertEquals(expected, input.matches(ValidationUtils.NULL_OR_NOT_BLANK));
+    }
+
+}