child_process: refactor string validation in exec and spawn

Author: puskin

lib/child_process.js

@@ -189,9 +189,6 @@ function _forkChild(fd, serializationMode) {
 }
 
 function normalizeExecArgs(command, options, callback) {
-  validateString(command, 'command');
-  validateArgumentNullCheck(command, 'command');
-
   if (typeof options === 'function') {
     callback = options;
     options = undefined;
@@ -568,9 +565,9 @@ let emittedDEP0190Already = false;
 function normalizeSpawnArguments(file, args, options) {
   validateString(file, 'file');
   validateArgumentNullCheck(file, 'file');
-
-  if (file.length === 0)
+  if (file.length === 0) {
     throw new ERR_INVALID_ARG_VALUE('file', file, 'cannot be empty');
+  }
 
   if (ArrayIsArray(args)) {
     args = ArrayPrototypeSlice(args);