Adjust on the attrs.get(ATTRIBUTE_PARAMS) process.

def paramsAttribute = attrs.get(ATTRIBUTE_PARAMS)
Map params = paramsAttribute && (paramsAttribute instanceof Map) ? (Map)paramsAttribute : null
if (params) 

Here, we have three steps to prepare our "params", but my suggestion is refactor this piece of code in a more groovy way.
With this update we avoid two step, we've got a little improvement of performance and a piece of code a little bit clean.

steps: 
1 - create: params Attribute
2 - check if params Attribute is true
3 - verify the type
4 - and cast to Map
5 - if false return null

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I think that here we can adjust for this:

def params = attrs.get(ATTRIBUTE_PARAMS)
if (params Map)

steps:
1 - create: params
2 - check if params is a Map
So, as groovy has a autocast for this kind of code, we just need to check if this guy is a Map and verify its boolean value.
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OBS: on the 152 line: We just need to check if paramsAttribute is a Map and Groovy will solve the rest.
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At the moment I don't have an environment for test this pull. So, please, if you will merge, just retest the "LinkGeneratorSpec.groovy".
Merge pull request #507 from jonatasemidio/patch-3

Adjust on the attrs.get(ATTRIBUTE_PARAMS) process.