ExternalProject: only append COMMAND if actually adding a command

Fixes #16544.

Modules/ExternalProject.cmake

@@ -1987,11 +1987,10 @@ function(_ep_add_download_command name)
         set(comment "Performing download step (${steps}) for '${name}'")
         _ep_write_verifyfile_script("${stamp_dir}/verify-${name}.cmake" "${file}" "${hash}")
       endif()
-      list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/verify-${name}.cmake
-        COMMAND)
+      list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/verify-${name}.cmake)
       if (NOT no_extract)
         _ep_write_extractfile_script("${stamp_dir}/extract-${name}.cmake" "${name}" "${file}" "${source_dir}")
-        list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/extract-${name}.cmake)
+        list(APPEND cmd COMMAND ${CMAKE_COMMAND} -P ${stamp_dir}/extract-${name}.cmake)
       else ()
         set_property(TARGET ${name} PROPERTY _EP_DOWNLOADED_FILE ${file})
       endif ()

Tests/ExternalProject/CMakeLists.txt

@@ -90,6 +90,16 @@ ExternalProject_Add(${proj}
 )
 set_property(TARGET ${proj} PROPERTY FOLDER "")
 
+set(proj NoExtractLogDownload)
+ExternalProject_Add(${proj}
+  URL ${CMAKE_CURRENT_SOURCE_DIR}/gitrepo.tgz
+  DOWNLOAD_NO_EXTRACT 1
+  LOG_DOWNLOAD 1
+  BUILD_COMMAND ""
+  CONFIGURE_COMMAND ""
+  INSTALL_COMMAND ""
+)
+
 
 # CVS-based tests:
 #