providers/aws: only flatten cidr if they exist

fixes #87

builtin/providers/aws/structure.go

@@ -111,7 +111,10 @@ func flattenIPPerms(list []ec2.IPPerm) []map[string]interface{} {
 		n["from_port"] = perm.FromPort
 		n["protocol"] = perm.Protocol
 		n["to_port"] = perm.ToPort
-		n["cidr_blocks"] = perm.SourceIPs
+
+		if len(perm.SourceIPs) > 0 {
+			n["cidr_blocks"] = perm.SourceIPs
+		}
 
 		if v := flattenSecurityGroups(perm.SourceGroups); len(v) > 0 {
 			n["security_groups"] = v

builtin/providers/aws/structure_test.go

@@ -155,6 +155,24 @@ func Test_flattenIPPerms(t *testing.T) {
 				},
 			},
 		},
+		{
+			Input: []ec2.IPPerm{
+				ec2.IPPerm{
+					Protocol:  "icmp",
+					FromPort:  1,
+					ToPort:    -1,
+					SourceIPs: nil,
+				},
+			},
+
+			Output: []map[string]interface{}{
+				map[string]interface{}{
+					"protocol":  "icmp",
+					"from_port": 1,
+					"to_port":   -1,
+				},
+			},
+		},
 	}
 
 	for _, tc := range cases {