Give the specification's JSON Builder error text with no sequence number

pipeline/pipeline.jsonbuilder/src/main/java/fiftyone/pipeline/jsonbuilder/flowelements/JsonBuilderElement.java

@@ -65,6 +65,13 @@ public class JsonBuilderElement
     private static final String JAVASCRIPT_PROPERTIES_NAME = "javascriptProperties";
     private static final String RAW_WEIGHTING_KEY = "rawweighting";
     private static final String VALUE_KEY = "value";
+    /**
+     * The error when no Sequence Element has produced a sequence number,
+     * worded as the specification gives it for every language.
+     */
+    private static final String NO_SEQUENCE_MESSAGE =
+        "The JSON Builder needs a sequence number. Place a Sequence Element " +
+        "before the JSON Builder in the Pipeline.";
     private final EvidenceKeyFilter evidenceKeyFilter;
     private final List<ElementPropertyMetaData> properties;
     private final List<String> blacklist;
@@ -203,9 +210,7 @@ private String buildJson(FlowData data, PipelineConfig config) throws Exception
         try {
           sequenceNumber = getSequenceNumber(data);
         } catch (Exception e) {
-            throw new PipelineConfigurationException("Make sure there is a "
-                    + "SequenceElement placed before this JsonBuilderElement "
-                    + "in the pipeline", e);
+            throw new PipelineConfigurationException(NO_SEQUENCE_MESSAGE, e);
         }
 
         Map<String, Object> allProperties = getAllProperties(data, config);
@@ -225,8 +230,7 @@ private int getSequenceNumber(FlowData data) throws Exception {
             "query.sequence",
             Integer.class);
         if(sequence.hasValue() == false) {
-            throw new Exception("Sequence number not present in evidence. " +
-                "this is mandatory.");
+            throw new Exception(NO_SEQUENCE_MESSAGE);
         }
         return sequence.getValue();
     }

pipeline/pipeline.jsonbuilder/src/test/java/fiftyone/pipeline/jsonbuilder/JsonBuilderSequenceMessageTests.java

@@ -0,0 +1,108 @@
+/* *********************************************************************
+ * This Original Work is copyright of 51 Degrees Mobile Experts Limited.
+ * Copyright 2026 51 Degrees Mobile Experts Limited, Davidson House,
+ * Forbury Square, Reading, Berkshire, United Kingdom RG1 3EU.
+ *
+ * This Original Work is licensed under the European Union Public Licence
+ * (EUPL) v.1.2 and is subject to its terms as set out below.
+ *
+ * If a copy of the EUPL was not distributed with this file, You can obtain
+ * one at https://opensource.org/licenses/EUPL-1.2.
+ *
+ * The 'Compatible Licences' set out in the Appendix to the EUPL (as may be
+ * amended by the European Commission) shall be deemed incompatible for
+ * the purposes of the Work and the provisions of the compatibility
+ * clause in Article 5 of the EUPL shall not apply.
+ *
+ * If using the Work as, or as part of, a network application, by
+ * including the attribution notice(s) required under Article 5 of the EUPL
+ * in the end user terms of the application under an appropriate heading,
+ * such notice(s) shall fulfill the requirements of that article.
+ * ********************************************************************* */
+
+package fiftyone.pipeline.jsonbuilder;
+
+import fiftyone.common.testhelpers.TestLoggerFactory;
+import fiftyone.pipeline.core.data.FlowData;
+import fiftyone.pipeline.core.data.FlowError;
+import fiftyone.pipeline.core.exceptions.PipelineConfigurationException;
+import fiftyone.pipeline.core.flowelements.Pipeline;
+import fiftyone.pipeline.core.flowelements.PipelineBuilder;
+import fiftyone.pipeline.exceptions.AggregateException;
+import fiftyone.pipeline.jsonbuilder.flowelements.JsonBuilderElementBuilder;
+import org.junit.jupiter.api.Test;
+import org.slf4j.ILoggerFactory;
+import org.slf4j.Logger;
+
+import java.util.Collection;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+/**
+ * With no Sequence Element before it, the JSON Builder fails with the message
+ * the specification gives, which is the same in every language.
+ * @see <a href="https://github.com/51Degrees/specifications/blob/main/pipeline-specification/pipeline-elements/json-builder.md#sequence-number">Specification</a>
+ */
+public class JsonBuilderSequenceMessageTests {
+    private static final String MESSAGE =
+        "The JSON Builder needs a sequence number. Place a Sequence Element " +
+        "before the JSON Builder in the Pipeline.";
+
+    private final TestLoggerFactory loggerFactory;
+
+    public JsonBuilderSequenceMessageTests() {
+        ILoggerFactory internalLogger = mock(ILoggerFactory.class);
+        when(internalLogger.getLogger(anyString()))
+            .thenReturn(mock(Logger.class));
+        loggerFactory = new TestLoggerFactory(internalLogger);
+    }
+
+    private Pipeline buildPipeline(boolean suppress) throws Exception {
+        return new PipelineBuilder(loggerFactory)
+            .addFlowElement(new JsonBuilderElementBuilder(loggerFactory).build())
+            .setAutoCloseElements(true)
+            .setSuppressProcessException(suppress)
+            .build();
+    }
+
+    /**
+     * The recorded error and its cause both carry the message.
+     */
+    @Test
+    public void JsonBuilder_NoSequenceElement_RecordedMessage()
+        throws Exception {
+        try (Pipeline pipeline = buildPipeline(true);
+             FlowData flowData = pipeline.createFlowData()) {
+            flowData.process();
+
+            Collection<FlowError> errors = flowData.getErrors();
+            assertEquals(1, errors.size());
+            Throwable error = errors.iterator().next().getThrowable();
+            assertInstanceOf(PipelineConfigurationException.class, error);
+            assertEquals(MESSAGE, error.getMessage());
+            assertEquals(MESSAGE, error.getCause().getMessage());
+        }
+    }
+
+    /**
+     * With exceptions not suppressed, the error the caller catches carries
+     * the message.
+     */
+    @Test
+    public void JsonBuilder_NoSequenceElement_ThrownMessage()
+        throws Exception {
+        try (Pipeline pipeline = buildPipeline(false);
+             FlowData flowData = pipeline.createFlowData()) {
+            AggregateException thrown = assertThrows(
+                AggregateException.class,
+                flowData::process);
+            assertEquals(1, thrown.getSuppressed().length);
+            assertEquals(MESSAGE, thrown.getSuppressed()[0].getMessage());
+        }
+    }
+}