Trim the string when cast string type to booleans

If TD is boolean, then
Case:
a) If SD is character string, then SV is replaced by
    TRIM ( BOTH ' ' FROM VE )
    Case:
    i) If the rules for literal in Subclause 5.3, “literal”, can be applied to SV to determine a valid
value of the data type TD, then let TV be that value.
   ii) Otherwise, an exception condition is raised: data exception — invalid character value for cast.
b) If SD is boolean, then TV is SV