[analyzer] dynamic_cast Simplify null value generation.
[analyzer] dynamic_cast Simplify null value generation.

As per Jordy's review. Creating a symbol here is more flexible; however
I could not come up with an example where it was needed. (What
constrains can be added on of the symbol constrained to 0?)

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@154542 91177308-0d34-0410-b5e6-96231b3b80d8

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