Fix exception for empty Table

Author: Brian Hulette

js/src/table.ts

@@ -101,7 +101,9 @@ export class Table implements DataFrame {
         }
         this.schema = schema;
         this.batches = batches;
-        this.batchesUnion = batches.reduce((union, batch) => union.concat(batch));
+        this.batchesUnion = batches.length == 0 ?
+            new RecordBatch(schema, 0, []) :
+            batches.reduce((union, batch) => union.concat(batch));
         this.length = this.batchesUnion.length;
         this.numCols = this.batchesUnion.numCols;
     }

js/test/unit/table-tests.ts

@@ -24,6 +24,10 @@ const {
 } = Arrow;
 
 describe(`Table`, () => {
+    test(`can create an empty table`, () => {
+        expect(Table.empty().length).toEqual(0)
+    });
+
     describe(`single record batch`, () => {
         const table = Table.from({
           'schema': {