Overwrite default config with CLI input even when the input value is …

…considered as empty

This change will fix two issues:
1. When CLI sets a flag to an empty value in Go, e.g. 0 as to Uint64, the flag will be skipped and never set correctly. This problem could be solved by using option "WithOverwriteWithEmptyValue" when merge two configs.
2. The default non-empty value in server config will be overwritten to an empty value after flag initialization. This problem is solved by explicitly providing default value to all flags that have a default value option.

internal/cli/server/config.go

@@ -956,14 +956,9 @@ func (c *Config) buildNode() (*node.Config, error) {
 
 func (c *Config) Merge(cc ...*Config) error {
 	for _, elem := range cc {
-		if err := mergo.Merge(c, elem, mergo.WithOverride, mergo.WithAppendSlice); err != nil {
+		if err := mergo.Merge(c, elem, mergo.WithOverwriteWithEmptyValue, mergo.WithAppendSlice); err != nil {
 			return fmt.Errorf("failed to merge configurations: %v", err)
 		}
-
-		// override max peers
-		if elem.P2P.MaxPeers == 0 {
-			c.P2P.MaxPeers = 0
-		}
 	}
 	return nil
 }

internal/cli/server/config_test.go

@@ -54,14 +54,11 @@ func TestConfigMerge(t *testing.T) {
 	}
 	expected := &Config{
 		Chain:      "1",
-		NoSnapshot: true,
+		NoSnapshot: false,
 		RequiredBlocks: map[string]string{
 			"a": "b",
 			"b": "c",
 		},
-		TxPool: &TxPoolConfig{
-			LifeTime: 5 * time.Second,
-		},
 		P2P: &P2PConfig{
 			MaxPeers: 10,
 			Discovery: &P2PDiscovery{