Steps to reproduce :

- create an audio mixer
- select the Attenuation
- right click on Volume in the Inspector and select expose
- select the Exposed Parameters option
- when "MyExposedParam" option is shown press ctrl +z and notice the error

IndexOutOfRangeException: Array index is out of range.
UnityEditor.AudioMixerExposedParameterView.GetInfoString (Int32 index) (at C:/buildslave/unity/build/Editor/Mono/Audio/Mixer/GUI/AudioMixerExposedParameterView.cs:116)
UnityEditor.AudioMixerExposedParameterView.WidthOfRow (Int32 index, UnityEngine.GUIStyle leftStyle, UnityEngine.GUIStyle rightStyle) (at C:/buildslave/unity/build/Editor/Mono/Audio/Mixer/GUI/AudioMixerExposedParameterView.cs:123)
UnityEditor.AudioMixerExposedParameterView.CalcSize () (at C:/buildslave/unity/build/Editor/Mono/Audio/Mixer/GUI/AudioMixerExposedParameterView.cs:107)
UnityEditor.AudioMixerExposedParametersPopup.GetWindowSize () (at C:/buildslave/unity/build/Editor/Mono/Audio/Mixer/GUI/AudioMixerExposedParametersPopup.cs:51)
UnityEditor.PopupWindow.FitWindowToContent () (at C:/buildslave/unity/build/Editor/Mono/GUI/PopupWindow.cs:89)
UnityEditor.PopupWindow.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/GUI/PopupWindow.cs:81)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:187)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:180)
UnityEditor.HostView.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:76)