Incorrect union generated code when using decimal64

Code generation fails when processing next yang input:

typedef cd-working-range-t {
type union {
type enumeration

{ enum "NA"; }

type decimal64

{ fraction-digits 2; range "-70000..70000"; }

}
}

• with following error:
  [ERROR] /C:/*/CdWorkingRangeT.java:[24,33] cannot find symbol
  [ERROR] symbol: method getValue()
  [ERROR] location: variable _decimal64 of type java.math.BigDecimal

BigDecimal doesn't have .getValue() method, so code generator should take this into account.

Problem was reported for Helium-SR4, but it persists even in Beryllium.