Resolve PR reviews

Author: AnandShivansh

hypertrace-core-graphql-span-schema/src/main/java/org/hypertrace/core/graphql/span/joiner/SpanJoiner.java

@@ -32,6 +32,16 @@ public <T> Single<ListMultimap<T, Span>> joinSpans(
         }
       };
 
+  default <T> Single<Map<T, Span>> joinSpan(
+      Collection<T> joinSources, SpanIdGetter<T> spanIdGetter) {
+    return joinSpan(joinSources, spanIdGetter, Collections.emptyList());
+  }
+
+  default <T> Single<ListMultimap<T, Span>> joinSpans(
+      Collection<T> joinSources, MultipleSpanIdGetter<T> multipleSpanIdGetter) {
+    return joinSpans(joinSources, multipleSpanIdGetter, Collections.emptyList());
+  }
+
   <T> Single<Map<T, Span>> joinSpan(
       Collection<T> joinSources,
       SpanIdGetter<T> spanIdGetter,