Validation error for 'null' values

[RazzM13]

Apparently, when cfn-lint encounters a null value in a template, it is unable to process it and throws an exception.

Steps to reproduce:

1. Create a test.yaml file that triggers a null value exception, perhaps with the following contents:

Resources:
  MyBucket:
    Type: 'AWS::S3::Bucket'
    Properties:
      Tags: null

2. Attempt to validate the file:
   cfn-lint validate test.yaml
3. Observe the output:
   validate.log

Expected: Processing to continue and a standard validation error to be displayed at the end.
Actual: An exceptions is logged ... uncaughtException: Cannot convert undefined or null to object ... and processing stops.