Replaced magic string with commented const

cmd/svcat/command/brokerfiltered.go

@@ -20,6 +20,11 @@ import (
 	"github.com/spf13/cobra"
 )
 
+const (
+	// BrokerAll is the default argument to specify when you want to list or filter resources for all brokers
+	BrokerAll string = ""
+)
+
 // HasBrokerFlag represents a command that supports --broker.
 type HasBrokerFlag interface {
 	// ApplyBrokerFlag validates and persists the broker related flag.

cmd/svcat/plan/get_cmd.go

@@ -138,7 +138,7 @@ func (c *GetCmd) getAll() error {
 		Namespace: c.Namespace,
 		Scope:     c.Scope,
 	}
-	classes, err := c.App.RetrieveClasses(classOpts, "")
+	classes, err := c.App.RetrieveClasses(classOpts, command.BrokerAll)
 	if err != nil {
 		return fmt.Errorf("unable to list classes (%s)", err)
 	}