How to generate full coverage data in out.json for all source files?

[WallaceChen123]

I am using babel-plugin-istanbul to generate code coverage report, however, I found that the out.json file only includes the coverage data for tested source files as below:
"C:\path\to\file\a.ts": {
"path": "C:\path\to\file\a.ts",
"statementMap": {
"0": {
"start": {
"line": 4,
"column": 2
},
"end": {
"line": 4,
"column": 116
}
},
......skip other data......
}

the coverage data for un-tested source files is missing as below:
"C:/path/to/file/b.ts": {
"path": "C:/path/to/file/b.ts",
"statementMap": {},
"fnMap": {},
"branchMap": {},
"s": {},
"f": {},
"b": {}
},
Based on the out.json file, the generated coverage report only displays coverage for the tested source files and ignores un-tested source files, so the total coverage is incorrect.

May I know is there any method to generate all coverage data in out.json for all source files including tested and un-tested source files? Thanks in advance.