Fix compilation error

Author: seanzhougoogle

delta-plugins-common/src/main/java/io/cdap/delta/plugin/mock/MockContext.java

@@ -22,10 +22,12 @@
 import io.cdap.delta.api.DeltaPipelineId;
 import io.cdap.delta.api.DeltaSourceContext;
 import io.cdap.delta.api.ReplicationError;
+import io.cdap.delta.api.SourceTable;
 
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 import javax.annotation.Nullable;
 
 /**
@@ -115,6 +117,11 @@ public DeltaPipelineId getPipelineId() {
     return new DeltaPipelineId("default", "app", 0L);
   }
 
+  @Override
+  public Set<SourceTable> getAllTables() {
+    return Collections.emptySet();
+  }
+
   @Override
   public PluginProperties getPluginProperties(String pluginId) {
     return PluginProperties.builder().build();