Revert "filter nulls when shimming a config"

This reverts commit 97bde5467c.

config/hcl2shim/values.go

@@ -167,10 +167,7 @@ func ConfigValueFromHCL2(v cty.Value) interface{} {
 		it := v.ElementIterator()
 		for it.Next() {
 			_, ev := it.Element()
-			cv := ConfigValueFromHCL2(ev)
-			if cv != nil {
-				l = append(l, cv)
-			}
+			l = append(l, ConfigValueFromHCL2(ev))
 		}
 		return l
 	}

config/hcl2shim/values_test.go

@@ -232,26 +232,6 @@ func TestConfigValueFromHCL2Block(t *testing.T) {
 			&configschema.Block{},
 			nil,
 		},
-		// nulls should be filtered out of the config, since they couldn't exist
-		// in hcl.
-		{
-			cty.ObjectVal(map[string]cty.Value{
-				"list": cty.ListVal([]cty.Value{
-					cty.StringVal("ok"),
-					cty.NullVal(cty.String)}),
-			}),
-			&configschema.Block{
-				Attributes: map[string]*configschema.Attribute{
-					"list": {
-						Type:     cty.List(cty.String),
-						Optional: true,
-					},
-				},
-			},
-			map[string]interface{}{
-				"list": []interface{}{"ok"},
-			},
-		},
 	}
 
 	for _, test := range tests {

helper/plugin/grpc_provider.go

@@ -1342,7 +1342,8 @@ func validateConfigNulls(v cty.Value, path cty.Path) []*proto.Diagnostic {
 			if ev.IsNull() {
 				diags = append(diags, &proto.Diagnostic{
 					Severity:  proto.Diagnostic_ERROR,
-					Summary:   "null value found in list",
+					Summary:   "Null value found in list",
+					Detail:    "Null values are not allowed for this attribute value.",
 					Attribute: convert.PathToAttributePath(append(path, cty.IndexStep{Key: kv})),
 				})
 				continue