StringUtils.join(Iterator, String) should only return null when the

Iterator is null

src/changes/changes.xml

@@ -90,6 +90,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action                   type="fix" dev="ggregory" due-to="guicaiyue">Javadoc: StringUtils.repeat("", "x", 3) = "xx"; #918.</action>
     <action                   type="fix" dev="ggregory" due-to="Marc Wrobel">Fix typos #920, #923.</action>
     <action                   type="fix" dev="ggregory" due-to="Bhimantoro Suryo Admodjo">Simplify condition #925.</action>
+    <action                   type="fix" dev="ggregory" due-to="Gary Gregory">StringUtils.join(Iterable, String) should only return null when the Iterable is null.</action>
     <action                   type="fix" dev="ggregory" due-to="Gary Gregory">StringUtils.join(Iterator, String) should only return null when the Iterator is null.</action>
     <!-- ADD -->
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add GitHub coverage.yml.</action>

src/main/java/org/apache/commons/lang3/StringUtils.java

@@ -4394,23 +4394,19 @@ public class StringUtils {
         if (!iterator.hasNext()) {
             return EMPTY;
         }
-        final Object first = iterator.next();
-        if (!iterator.hasNext()) {
-            return toStringOrEmpty(first);
-        }
 
         // two or more elements
         final StringBuilder buf = new StringBuilder(STRING_BUILDER_SIZE); // Java default is 16, probably too small
-        if (first != null) {
-            buf.append(first);
-        }
 
         while (iterator.hasNext()) {
-            buf.append(separator);
             final Object obj = iterator.next();
             if (obj != null) {
                 buf.append(obj);
             }
+            if (iterator.hasNext()) {
+                buf.append(separator);
+            }
+
         }
 
         return buf.toString();

src/test/java/org/apache/commons/lang3/StringUtilsTest.java

@@ -1292,6 +1292,7 @@ public class StringUtilsTest extends AbstractLangTest {
         assertEquals("", StringUtils.join(Arrays.asList(NULL_ARRAY_LIST).iterator(), SEPARATOR_CHAR));
         assertEquals("", StringUtils.join(Arrays.asList(EMPTY_ARRAY_LIST).iterator(), SEPARATOR_CHAR));
         assertEquals("foo", StringUtils.join(Collections.singleton("foo").iterator(), 'x'));
+        assertEquals("null", StringUtils.join(Arrays.asList(NULL_TO_STRING_LIST).iterator(), SEPARATOR_CHAR));
     }
 
     @Test