[PORT] Support empty lg file. (#2109)

libraries/botbuilder-lg/src/templatesParser.ts

@@ -203,7 +203,7 @@ export class TemplatesParser {
     }
 
     private static antlrParseTemplates(text: string, source: string): FileContext {
-        if (!text) {
+        if (!text || text.trim() === '') {
             return undefined;
         }
 
@@ -230,7 +230,10 @@ class TemplatesTransformer extends AbstractParseTreeVisitor<any> implements LGTe
     }
 
     public transform(parseTree: ParseTree): Templates {
-        this.visit(parseTree);
+        if (parseTree) {
+            this.visit(parseTree);
+        }
+
         return this.templates;
     }
 

libraries/botbuilder-lg/tests/lgDiagnostic.test.js

@@ -74,7 +74,7 @@ describe(`LGExceptionTest`, function() {
         assert.strictEqual(diagnostics[1].message.includes(`Duplicated definitions found for template: 'basicTemplate2'`), true);
     });
 
-    it(`TestEmptyLGFile`, function() {
+    it(`TestEmptyTemplate`, function() {
         var diagnostics = GetDiagnostics(`EmptyTemplate.lg`);
 
         assert.strictEqual(1, diagnostics.length);
@@ -82,6 +82,14 @@ describe(`LGExceptionTest`, function() {
         assert.strictEqual(diagnostics[0].message.includes(TemplateErrors.noTemplateBody('template')), true);
     });
 
+    it(`TestEmptyLGFile`, function() {
+        var diagnostics = GetDiagnostics(`EmptyLGFile.lg`);
+
+        assert.strictEqual(1, diagnostics.length);
+        assert.strictEqual(DiagnosticSeverity.Warning, diagnostics[0].severity);
+        assert.strictEqual(diagnostics[0].message.includes(TemplateErrors.noTemplate), true);
+    });
+
     it(`TestErrorStructuredTemplate`, function() {
         var diagnostics = GetDiagnostics(`ErrorStructuredTemplate.lg`);
 

libraries/botbuilder-lg/tests/testData/exceptionExamples/EmptyLGFile.lg

@@ -1 +0,0 @@
-> should throw WRAN