Test: Fix dv date bwc tests when no docs have a value (#32798)

This commit adds a guard around the rare case that no documents in the
10 iterations actually have any values, thus making the warning check
incorrect.

closes #32779

Author: rjernst

server/src/test/java/org/elasticsearch/index/fielddata/ScriptDocValuesDatesTests.java

@@ -88,13 +88,15 @@ public void assertDateDocValues(boolean useJavaTime, String... expectedWarnings)
             }
         );
 
+        boolean valuesExist = false;
         for (int round = 0; round < 10; round++) {
             int d = between(0, values.length - 1);
             dates.setNextDocId(d);
             Object dateValue = AccessController.doPrivileged((PrivilegedAction<Object>) dates::getValue, noPermissionsAcc);
             assertEquals(expectedDates[d].length > 0 ? expectedDates[d][0] : new DateTime(0, DateTimeZone.UTC), dateValue);
             Object bwcDateValue = AccessController.doPrivileged((PrivilegedAction<Object>) dates::getDate, noPermissionsAcc);
             assertEquals(expectedDates[d].length > 0 ? expectedDates[d][0] : new DateTime(0, DateTimeZone.UTC), bwcDateValue);
+            valuesExist |= expectedDates[d].length > 0;
 
             AccessController.doPrivileged((PrivilegedAction<Object>) dates::getDates, noPermissionsAcc);
             assertEquals(values[d].length, dates.size());
@@ -107,7 +109,9 @@ public void assertDateDocValues(boolean useJavaTime, String... expectedWarnings)
         // using "hasItems" here instead of "containsInAnyOrder",
         // because values are randomly initialized, sometimes some of docs will not have any values
         // and warnings in this case will contain another deprecation warning on missing values
-        assertThat(warnings, hasItems(expectedWarnings));
+        if (valuesExist) {
+            assertThat(warnings, hasItems(expectedWarnings));
+        }
     }
 
     private Dates wrap(long[][] values, BiConsumer<String, String> deprecationHandler, boolean useJavaTime) {