Support EMPTYSTR in jison parser, add unit tests for git graph parser

src/diagrams/git/gitGraphParserV2.spec.js

@@ -627,6 +627,38 @@ describe('when parsing a gitGraph', function () {
     expect(commits[cherryPickCommitID].branch).toBe('main');
   });
 
+  it('should support cherry-picking commits with custom tag', function () {
+    const str = `gitGraph
+    commit id: "ZERO"
+    branch develop
+    commit id:"A"
+    checkout main
+    cherry-pick id:"A" tag:"MyTag"
+    `;
+
+    parser.parse(str);
+    const commits = parser.yy.getCommits();
+    const cherryPickCommitID = Object.keys(commits)[2];
+    expect(commits[cherryPickCommitID].tag).toBe('MyTag');
+    expect(commits[cherryPickCommitID].branch).toBe('main');
+  });
+
+  it('should support cherry-picking commits with no tag', function () {
+    const str = `gitGraph
+    commit id: "ZERO"
+    branch develop
+    commit id:"A"
+    checkout main
+    cherry-pick id:"A" tag:""
+    `;
+
+    parser.parse(str);
+    const commits = parser.yy.getCommits();
+    const cherryPickCommitID = Object.keys(commits)[2];
+    expect(commits[cherryPickCommitID].tag).toBe('');
+    expect(commits[cherryPickCommitID].branch).toBe('main');
+  });
+
   it('should throw error when try to branch existing branch: main', function () {
     const str = `gitGraph
     commit

src/diagrams/git/parser/gitGraph.jison

@@ -57,6 +57,7 @@ checkout(?=\s|$)                        return 'CHECKOUT';
 "options"\r?\n                          this.begin("options"); //
 <options>[ \r\n\t]+"end"                this.popState();       // not used anymore in the renderer, fixed for backward compatibility
 <options>[\s\S]+(?=[ \r\n\t]+"end")     return 'OPT';          //
+["]["]                                  return 'EMPTYSTR';
 ["]                                     this.begin("string");
 <string>["]                             this.popState();
 <string>[^"]*                           return 'STR';
@@ -119,7 +120,9 @@ branchStatement
 cherryPickStatement
     : CHERRY_PICK COMMIT_ID STR {yy.cherryPick($3, '', undefined)}
     | CHERRY_PICK COMMIT_ID STR COMMIT_TAG STR {yy.cherryPick($3, '', $5)}
+    | CHERRY_PICK COMMIT_ID STR COMMIT_TAG EMPTYSTR {yy.cherryPick($3, '', '')}
     | CHERRY_PICK COMMIT_TAG STR COMMIT_ID STR {yy.cherryPick($5, '', $3)}
+    | CHERRY_PICK COMMIT_TAG EMPTYSTR COMMIT_ID STR {yy.cherryPick($3, '', '')}
     ;
 
 mergeStatement