Check for null RoleDefinitionName in GetAzureRoleAssignmentCommand

Added tests for GetAzRoleAssingments using only the role name
Fix tests
Add region for parameter in GetAzureRoleAssignmentCommand

Author: dagoroz

src/Resources/Resources.Test/ScenarioTests/RoleAssignmentTests.cs

@@ -1,4 +1,4 @@
-// ----------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------
 //
 // Copyright Microsoft Corporation
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -159,6 +159,13 @@ public void RaGetByScope()
             TestRunner.RunTestScript("Test-RaGetByScope");
         }
 
+        [Fact(Skip = "Needs recording. PS-VSPrompt link and TestFramework are broken at time of commit")]
+        [Trait(Category.AcceptanceType, Category.CheckIn)]
+        public void RaGetOnlyByRoleDefinitionName()
+        {
+            TestRunner.RunTestScript("Test-RaGetOnlyByRoleDefinitionName");
+        }
+
         [Fact]
         [Trait(Category.AcceptanceType, Category.CheckIn)]
         public void RaGetByUPNWithExpandPrincipalGroups()

src/Resources/Resources.Test/ScenarioTests/RoleAssignmentTests.ps1

@@ -639,6 +639,21 @@ function Test-RaGetByScope
     VerifyRoleAssignmentDeleted $newAssignment1
 }
 
+<#
+.SYNOPSIS
+Tests verifies get of RoleAssignment using only the role definition name
+#>
+function Test-RaGetOnlyByRoleDefinitionName
+{
+    # Setup
+    $definitionName = 'Owner'
+    
+    $ras = Get-AzRoleAssignment -RoleDefinitionName $definitionName
+
+    Assert-NotNull $ras
+    Assert-AreEqual $definitionName $ras[0].RoleDefinitionName
+}
+
 <#
 .SYNOPSIS
 Creates role assignment

src/Resources/Resources/Models.Authorization/AuthorizationClient.cs

@@ -226,7 +226,7 @@ public List<PSRoleAssignment> FilterRoleAssignments(FilterRoleAssignmentsOptions
 
             if (!string.IsNullOrEmpty(options.RoleDefinitionName))
             {
-                result = result.Where(r => r.RoleDefinitionName.Equals(options.RoleDefinitionName, StringComparison.OrdinalIgnoreCase)).ToList();
+                result = result.Where(r => r.RoleDefinitionName?.Equals(options.RoleDefinitionName, StringComparison.OrdinalIgnoreCase) ?? false).ToList();
             }
 
             if (options.IncludeClassicAdministrators)

src/Resources/Resources/RoleAssignments/GetAzureRoleAssignmentCommand.cs

@@ -29,6 +29,8 @@ namespace Microsoft.Azure.Commands.Resources
     [Cmdlet("Get", ResourceManager.Common.AzureRMConstants.AzureRMPrefix + "RoleAssignment", DefaultParameterSetName = ParameterSet.Empty), OutputType(typeof(PSRoleAssignment))]
     public class GetAzureRoleAssignmentCommand : ResourcesBaseCmdlet
     {
+        #region Cmdlet Parameters
+
         [Parameter(Mandatory = true, ValueFromPipelineByPropertyName = true, ParameterSetName = ParameterSet.ObjectId,
             HelpMessage = "The user or group object id.")]
         [Parameter(Mandatory = true, ValueFromPipelineByPropertyName = true, ParameterSetName = ParameterSet.ResourceGroupWithObjectId,
@@ -214,6 +216,9 @@ public class GetAzureRoleAssignmentCommand : ResourcesBaseCmdlet
             HelpMessage = "If specified, also returns the subscription classic administrators as role assignments.")]
         public SwitchParameter IncludeClassicAdministrators { get; set; }
 
+        #endregion
+
+
         public override void ExecuteCmdlet()
         {
             FilterRoleAssignmentsOptions options = new FilterRoleAssignmentsOptions()