Description of problem:
In the Guided rules editor, facts and fields can be bound to variables. The only way to remove that binding is to bind it to a new variable that is an empty string. This causes some problem with the rule source.
After removing the variable from a fact, the corresponding row in the source looks like this: 
  when  
          : fact(/*whatever was matched here*/)
  then
The colon after the variable is still there, even if there's no variable now (except for the empty string and that shouldn't count). If it was on the first line, you can still validate the rule and it will be ok. More problems show, when you do the same thing to a fact on another line or when you remove a binding form a field. Validation then returns an error message containing something like: 
  [<rule>] [ERR 102] Line x:y mismatched input ':' in rule "<rule>"
  [<rule>] Parser returned a null Package


Version-Release number of selected component (if applicable):
BRMS 5.2.0 ER5


Steps to Reproduce:
1. Add a Fact to a rule,
2. add another fact, add a field to it.
3. Bind a) a valid variable or b) an empty string variable to the 2nd fact and another to its field.
4a. Rewrite the binding with an empty string for the a) second fact or b) its field.

Validate.

  
Actual results:
Error message
  [<rule>] [ERR 102] Line x:y mismatched input ':' in rule "<rule>"
  [<rule>] Parser returned a null Package


Expected results:
Rule validated ok.


Additional info:
It should be enough to just test the variable string for an empty string before setting anything and removing the variable and the colon when it is empty.