Remove redundant checks in runconfig.Merge

Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)

runconfig/merge.go

@@ -20,7 +20,7 @@ func Merge(userConf, imageConf *Config) error {
 	if userConf.CpuShares == 0 {
 		userConf.CpuShares = imageConf.CpuShares
 	}
-	if userConf.ExposedPorts == nil || len(userConf.ExposedPorts) == 0 {
+	if len(userConf.ExposedPorts) == 0 {
 		userConf.ExposedPorts = imageConf.ExposedPorts
 	} else if imageConf.ExposedPorts != nil {
 		if userConf.ExposedPorts == nil {
@@ -33,7 +33,7 @@ func Merge(userConf, imageConf *Config) error {
 		}
 	}
 
-	if userConf.PortSpecs != nil && len(userConf.PortSpecs) > 0 {
+	if len(userConf.PortSpecs) > 0 {
 		if userConf.ExposedPorts == nil {
 			userConf.ExposedPorts = make(nat.PortSet)
 		}
@@ -48,7 +48,7 @@ func Merge(userConf, imageConf *Config) error {
 		}
 		userConf.PortSpecs = nil
 	}
-	if imageConf.PortSpecs != nil && len(imageConf.PortSpecs) > 0 {
+	if len(imageConf.PortSpecs) > 0 {
 		// FIXME: I think we can safely remove this. Leaving it for now for the sake of reverse-compat paranoia.
 		utils.Debugf("Migrating image port specs to containter: %s", strings.Join(imageConf.PortSpecs, ", "))
 		if userConf.ExposedPorts == nil {
@@ -66,7 +66,7 @@ func Merge(userConf, imageConf *Config) error {
 		}
 	}
 
-	if userConf.Env == nil || len(userConf.Env) == 0 {
+	if len(userConf.Env) == 0 {
 		userConf.Env = imageConf.Env
 	} else {
 		for _, imageEnv := range imageConf.Env {
@@ -84,16 +84,16 @@ func Merge(userConf, imageConf *Config) error {
 		}
 	}
 
-	if userConf.Cmd == nil || len(userConf.Cmd) == 0 {
+	if len(userConf.Cmd) == 0 {
 		userConf.Cmd = imageConf.Cmd
 	}
-	if userConf.Entrypoint == nil || len(userConf.Entrypoint) == 0 {
+	if len(userConf.Entrypoint) == 0 {
 		userConf.Entrypoint = imageConf.Entrypoint
 	}
 	if userConf.WorkingDir == "" {
 		userConf.WorkingDir = imageConf.WorkingDir
 	}
-	if userConf.Volumes == nil || len(userConf.Volumes) == 0 {
+	if len(userConf.Volumes) == 0 {
 		userConf.Volumes = imageConf.Volumes
 	} else {
 		for k, v := range imageConf.Volumes {