ensure name is at lest 1 char

Signed-off-by: jowg-amazon <[email protected]>

src/main/kotlin/org/opensearch/commons/alerting/model/DocLevelQuery.kt

@@ -80,7 +80,7 @@ data class DocLevelQuery(
         const val QUERY_FIELD_NAMES_FIELD = "query_field_names"
         const val NO_ID = ""
         val INVALID_CHARACTERS: List<String> = listOf(" ", "[", "]", "{", "}", "(", ")")
-        val QUERY_NAME_REGEX = "^.{0,256}$".toRegex() // regex to restrict string length 256 chars
+        val QUERY_NAME_REGEX = "^.{1,256}$".toRegex() // regex to restrict string length between 1 - 256 chars
 
         @JvmStatic
         @Throws(IOException::class)

src/test/kotlin/org/opensearch/commons/alerting/model/DocLevelMonitorInputTests.kt

@@ -44,6 +44,20 @@ class DocLevelMonitorInputTests {
     @Test
     fun `test create Doc Level Query with invalid name length`() {
         val stringBuilder = StringBuilder()
+
+        // test empty string
+        val emptyString = stringBuilder.toString()
+        try {
+            randomDocLevelQuery(name = emptyString)
+            Assertions.fail("Expecting an illegal argument exception")
+        } catch (e: IllegalArgumentException) {
+            Assertions.assertEquals(
+                "The query name, $emptyString, can be max 256 characters.",
+                e.message
+            )
+        }
+
+        // test string with 257 chars
         repeat(257) {
             stringBuilder.append("a")
         }