code: public boolean isGlobalVariable(@Nullable final String variableName) {
      boolean result = false;
      if (variableName != null) {
        final String normalized = PreprocessorUtils.normalizeVariableName(variableName);
        result = this.globalVarTable.containsKey(normalized) || mapVariableNameToSpecialVarProcessor.containsKey(normalized);
      }
      return result;
    }
docs: Check that there is a global variable with such name.
  
  @param variableName a name to be checked, can be null
  @return false if there is not such variable or it is null, true if such global or special variable exists