[BUG] add consistency to_numeric on empty list

pandas/core/tools/numeric.py

@@ -162,7 +162,7 @@ def to_numeric(arg, errors="raise", downcast=None):
 
         if downcast in ("integer", "signed"):
             typecodes = np.typecodes["Integer"]
-        elif downcast == "unsigned" and np.min(values) >= 0:
+        elif downcast == "unsigned" and np.min(values, initial=0) >= 0:
             typecodes = np.typecodes["UnsignedInteger"]
         elif downcast == "float":
             typecodes = np.typecodes["Float"]

pandas/tests/tools/test_to_numeric.py

@@ -627,3 +627,12 @@ def test_non_coerce_uint64_conflict(errors, exp):
     else:
         result = to_numeric(ser, errors=errors)
         tm.assert_series_equal(result, ser)
+
+
+def test_downcast_empty():
+    dc_int = pd.to_numeric([], downcast="integer")
+    dc_float = pd.to_numeric([], downcast="float")
+    dc_us = pd.to_numeric([], downcast="unsigned")
+
+    assert np.array_equal(dc_int, dc_float)
+    assert np.array_equal(dc_us, dc_float)