diff --git a/x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtil.java b/x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtil.java
index 0c839ba7995..2892637a5c3 100644
--- a/x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtil.java
+++ b/x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtil.java
@@ -24,6 +24,7 @@ import org.elasticsearch.xpack.core.ClientHelper;
 import org.elasticsearch.xpack.core.transform.transforms.pivot.PivotConfig;
 
 import java.math.BigDecimal;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
@@ -249,12 +250,11 @@ public final class SchemaUtil {
     /*
      * Very "magic" helper method to extract the source mappings
      */
-    private static void getSourceFieldMappings(
-        Client client,
-        String[] index,
-        String[] fields,
-        ActionListener<Map<String, String>> listener
-    ) {
+    static void getSourceFieldMappings(Client client, String[] index, String[] fields, ActionListener<Map<String, String>> listener) {
+        if (index == null || index.length == 0 || fields == null || fields.length == 0) {
+            listener.onResponse(Collections.emptyMap());
+            return;
+        }
         FieldCapabilitiesRequest fieldCapabilitiesRequest = new FieldCapabilitiesRequest().indices(index)
             .fields(fields)
             .indicesOptions(IndicesOptions.LENIENT_EXPAND_OPEN);
diff --git a/x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtilTests.java b/x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtilTests.java
index 1aa803e109e..84aa2e55bf5 100644
--- a/x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtilTests.java
+++ b/x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/pivot/SchemaUtilTests.java
@@ -6,11 +6,27 @@
 
 package org.elasticsearch.xpack.transform.transforms.pivot;
 
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.ActionRequest;
+import org.elasticsearch.action.ActionResponse;
+import org.elasticsearch.action.ActionType;
+import org.elasticsearch.action.LatchedActionListener;
+import org.elasticsearch.action.fieldcaps.FieldCapabilities;
+import org.elasticsearch.action.fieldcaps.FieldCapabilitiesRequest;
+import org.elasticsearch.action.fieldcaps.FieldCapabilitiesResponse;
+import org.elasticsearch.client.Client;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.client.NoOpClient;
 
 import java.math.BigInteger;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
 
 import static org.hamcrest.CoreMatchers.instanceOf;
 
@@ -69,4 +85,114 @@ public class SchemaUtilTests extends ESTestCase {
         assertEquals(new BigInteger("18446744073709551615").doubleValue(), ((BigInteger) value).doubleValue(), 0.0);
     }
 
+    public void testGetSourceFieldMappings() throws InterruptedException {
+        try (Client client = new FieldCapsMockClient(getTestName())) {
+            // fields is null
+            this.<Map<String, String>>assertAsync(
+                listener -> SchemaUtil.getSourceFieldMappings(client, new String[] { "index-1", "index-2" }, null, listener),
+                mappings -> {
+                    assertNotNull(mappings);
+                    assertTrue(mappings.isEmpty());
+                }
+            );
+
+            // fields is empty
+            this.<Map<String, String>>assertAsync(
+                listener -> SchemaUtil.getSourceFieldMappings(client, new String[] { "index-1", "index-2" }, new String[] {}, listener),
+                mappings -> {
+                    assertNotNull(mappings);
+                    assertTrue(mappings.isEmpty());
+                }
+            );
+
+            // indices is null
+            this.<Map<String, String>>assertAsync(
+                listener -> SchemaUtil.getSourceFieldMappings(client, null, new String[] { "field-1", "field-2" }, listener),
+                mappings -> {
+                    assertNotNull(mappings);
+                    assertTrue(mappings.isEmpty());
+                }
+            );
+
+            // indices is empty
+            this.<Map<String, String>>assertAsync(
+                listener -> SchemaUtil.getSourceFieldMappings(client, new String[] {}, new String[] { "field-1", "field-2" }, listener),
+                mappings -> {
+                    assertNotNull(mappings);
+                    assertTrue(mappings.isEmpty());
+                }
+            );
+
+            // good use
+            this.<Map<String, String>>assertAsync(
+                listener -> SchemaUtil.getSourceFieldMappings(
+                    client,
+                    new String[] { "index-1", "index-2" },
+                    new String[] { "field-1", "field-2" },
+                    listener
+                ),
+                mappings -> {
+                    assertNotNull(mappings);
+                    assertEquals(2, mappings.size());
+                    assertEquals("long", mappings.get("field-1"));
+                    assertEquals("long", mappings.get("field-2"));
+                }
+            );
+        }
+    }
+
+    private static class FieldCapsMockClient extends NoOpClient {
+        FieldCapsMockClient(String testName) {
+            super(testName);
+        }
+
+        @SuppressWarnings("unchecked")
+        @Override
+        protected <Request extends ActionRequest, Response extends ActionResponse> void doExecute(
+            ActionType<Response> action,
+            Request request,
+            ActionListener<Response> listener
+        ) {
+            if (request instanceof FieldCapabilitiesRequest) {
+                FieldCapabilitiesRequest fieldCapsRequest = (FieldCapabilitiesRequest) request;
+                Map<String, Map<String, FieldCapabilities>> responseMap = new HashMap<>();
+                for (String field : fieldCapsRequest.fields()) {
+                    responseMap.put(field, Collections.singletonMap(field, createFieldCapabilities(field, "long")));
+                }
+
+                final FieldCapabilitiesResponse response = new FieldCapabilitiesResponse(fieldCapsRequest.indices(), responseMap);
+                listener.onResponse((Response) response);
+                return;
+            }
+
+            super.doExecute(action, request, listener);
+        }
+    }
+
+    private static FieldCapabilities createFieldCapabilities(String name, String type) {
+        return new FieldCapabilities(
+            name,
+            type,
+            true,
+            true,
+            Strings.EMPTY_ARRAY,
+            Strings.EMPTY_ARRAY,
+            Strings.EMPTY_ARRAY,
+            Collections.emptyMap()
+        );
+    }
+
+    private <T> void assertAsync(Consumer<ActionListener<T>> function, Consumer<T> furtherTests) throws InterruptedException {
+        CountDownLatch latch = new CountDownLatch(1);
+        AtomicBoolean listenerCalled = new AtomicBoolean(false);
+
+        LatchedActionListener<T> listener = new LatchedActionListener<>(ActionListener.wrap(r -> {
+            assertTrue("listener called more than once", listenerCalled.compareAndSet(false, true));
+            furtherTests.accept(r);
+        }, e -> { fail("got unexpected exception: " + e); }), latch);
+
+        function.accept(listener);
+        assertTrue("timed out after 20s", latch.await(20, TimeUnit.SECONDS));
+    }
+
 }