fix pip module for 10.0.0

Fixes #46971

salt/modules/pip.py

@@ -798,6 +798,11 @@ def install(pkgs=None,  # pylint: disable=R0912,R0913,R0914
         # Put the commas back in while making sure the names are contained in
         # quotes, this allows for proper version spec passing salt>=0.17.0
         cmd.extend(['{0}'.format(p.replace(';', ',')) for p in pkgs])
+    else:
+        # Starting with pip 10.0.0, if no packages are specified in the
+        # command, it returns a retcode 1.  So instead of running the command,
+        # just return the output without running pip.
+        return {'retcode': 0, 'stdout': 'No packages to install.'}
 
     if editable:
         egg_match = re.compile(r'(?:#|#.*?&)egg=([^&]*)')