Program: 91721
Project: 91721
Buggy source:
/** 
 * Encodes the given position into a MGRS reference. It is caller responsibility to ensure that the position CRS is the same than the CRS specified at this   {@code Encoder} creation time.
 * @param owner      the {@code Coder} which own this {@code Encoder}.
 * @param position   the direct position to format as a MGRS reference.
 * @param reproject  whether this method is allowed to reproject {@code position} when needed.
 * @param separator  the separator to insert between each component of the MGRS identifier.
 * @param digits     number of digits to use for formatting the numerical part of a MGRS reference.
 * @return the value of {@code buffer.toString()}, or   {@code null} if a reprojection was necessarybut  {@code reproject} is {@code false}.
 */
String encode(final Coder owner,DirectPosition position,final boolean reproject,final String separator,final int digits) throws FactoryException, TransformException {
  final StringBuilder buffer=owner.buffer;
  if (toNormalized != null) {
    owner.normalized=position=toNormalized.transform(position,owner.normalized);
  }
  final DirectPosition geographic=toGeographic.transform(position,owner.geographic);
  owner.geographic=geographic;
  final double λ=geographic.getOrdinate(1);
  final double φ=geographic.getOrdinate(0);
  final boolean isUTM=φ >= TransverseMercator.Zoner.SOUTH_BOUNDS && φ < TransverseMercator.Zoner.NORTH_BOUNDS;
  final int zone=isUTM ? ZONER.zone(φ,λ) : POLE;
  final int signedZone=MathFunctions.isNegative(φ) ? -zone : zone;
  if (signedZone == 0) {
    throw new GazetteerException(Errors.format(Errors.Keys.NotANumber_1,"String_Node_Str"));
  }
  if (signedZone != crsZone) {
    if (!reproject) {
      return null;
    }
    if (signedZone != actualZone) {
      actualZone=0;
      toActualZone=CRS.findOperation(datum.geographic(),datum.universal(φ,λ),null).getMathTransform();
      actualZone=signedZone;
    }
    owner.normalized=position=toActualZone.transform(geographic,owner.normalized);
  }
  buffer.setLength(0);
  if (isUTM) {
    buffer.append(zone).append(separator).append(latitudeBand(φ));
  }
 else {
    char z=(signedZone < 0) ? 'A' : 'Y';
    if (λ >= 0)     z++;
    buffer.append(z);
  }
  if (digits >= 0) {
    final double x=position.getOrdinate(0);
    final double y=position.getOrdinate(1);
    final double cx=Math.floor(x / GRID_SQUARE_SIZE);
    final double cy=Math.floor(y / GRID_SQUARE_SIZE);
    int col=(int)cx;
    int row=(int)cy;
    if (isUTM) {
      if (col < 1 || col > 8) {
        throw new GazetteerException(Errors.format(Errors.Keys.OutsideDomainOfValidity));
      }
switch (zone % 3) {
case 1:
        col+=('A' - 1);
      break;
case 2:
    col+=('J' - 1);
  if (col >= EXCLUDE_O)   col++;
break;
case 0:
col+=('S' - 1);
break;
}
if ((zone & 1) == 0) {
row+=('F' - 'A');
}
row%=GRID_ROW_COUNT;
}
 else {
final byte[] columns=POLAR_COLUMNS;
col-=(int)(PolarStereographicA.UPS_SHIFT / GRID_SQUARE_SIZE);
if (!(λ >= 0)) {
col+=columns.length;
}
if (col < 0 || col >= columns.length) {
throw new GazetteerException(Errors.format(Errors.Keys.OutsideDomainOfValidity));
}
col=columns[col];
row-=owner.getReferenceSystem().polarOffset(signedZone < 0);
}
row+='A';
if (row >= EXCLUDE_I && ++row >= EXCLUDE_O) row++;
buffer.append(separator).append(letter(col)).append(letter(row));
if (digits > 0) {
final double precision=MathFunctions.pow10(METRE_PRECISION_DIGITS - digits);
append(buffer.append(separator),(int)((x - cx * GRID_SQUARE_SIZE) / precision),digits);
append(buffer.append(separator),(int)((y - cy * GRID_SQUARE_SIZE) / precision),digits);
}
}
return buffer.toString();
}

Fixed version (ground truth):
/** 
 * Encodes the given position into a MGRS reference. It is caller responsibility to ensure that the position CRS is the same than the CRS specified at this   {@code Encoder} creation time.
 * @param owner      the {@code Coder} which own this {@code Encoder}.
 * @param position   the direct position to format as a MGRS reference.
 * @param reproject  whether this method is allowed to reproject {@code position} when needed.
 * @param separator  the separator to insert between each component of the MGRS identifier.
 * @param digits     number of digits to use for formatting the numerical part of a MGRS reference.
 * @return the value of {@code buffer.toString()}, or   {@code null} if a reprojection was necessarybut  {@code reproject} is {@code false}.
 */
String encode(final Coder owner,DirectPosition position,final boolean reproject,final String separator,final int digits) throws FactoryException, TransformException {
  final StringBuilder buffer=owner.buffer;
  if (toNormalized != null) {
    owner.normalized=position=toNormalized.transform(position,owner.normalized);
  }
  final DirectPosition geographic=toGeographic.transform(position,owner.geographic);
  owner.geographic=geographic;
  final double λ=geographic.getOrdinate(1);
  final double φ=geographic.getOrdinate(0);
  final boolean isUTM=φ >= TransverseMercator.Zoner.SOUTH_BOUNDS && φ < TransverseMercator.Zoner.NORTH_BOUNDS;
  final int zone=isUTM ? ZONER.zone(φ,λ) : POLE;
  final int signedZone=MathFunctions.isNegative(φ) ? -zone : zone;
  if (signedZone == 0) {
    throw new GazetteerException(Errors.format(Errors.Keys.NotANumber_1,"String_Node_Str"));
  }
  if (signedZone != crsZone) {
    if (!reproject) {
      return null;
    }
    if (signedZone != actualZone) {
      actualZone=0;
      toActualZone=CRS.findOperation(datum.geographic(),datum.universal(φ,λ),null).getMathTransform();
      actualZone=signedZone;
    }
    owner.normalized=position=toActualZone.transform(geographic,owner.normalized);
  }
  buffer.setLength(0);
  if (isUTM) {
    buffer.append(zone).append(separator).append(latitudeBand(φ));
  }
 else {
    char z=(signedZone < 0) ? 'A' : 'Y';
    if (λ >= 0)     z++;
    buffer.append(z);
  }
  if (digits >= 0) {
    final double x=position.getOrdinate(0);
    final double y=position.getOrdinate(1);
    final double cx=Math.floor(x / GRID_SQUARE_SIZE);
    final double cy=Math.floor(y / GRID_SQUARE_SIZE);
    int col=(int)cx;
    int row=(int)cy;
    if (isUTM) {
      if (col < 1 || col > 8) {
        throw new GazetteerException(Errors.format(Errors.Keys.OutsideDomainOfValidity));
      }
switch (zone % 3) {
case 1:
        col+=('A' - 1);
      break;
case 2:
    col+=('J' - 1);
  if (col >= EXCLUDE_O)   col++;
break;
case 0:
col+=('S' - 1);
break;
}
if ((zone & 1) == 0) {
row+=('F' - 'A');
}
row%=GRID_ROW_COUNT;
}
 else {
final byte[] columns=POLAR_COLUMNS;
col-=PolarStereographicA.UPS_SHIFT / GRID_SQUARE_SIZE;
if (!(λ >= 0)) {
col+=columns.length;
}
if (col < 0 || col >= columns.length) {
throw new GazetteerException(Errors.format(Errors.Keys.OutsideDomainOfValidity));
}
col=columns[col];
row-=owner.getReferenceSystem().polarOffset(signedZone < 0);
}
row+='A';
if (row >= EXCLUDE_I && ++row >= EXCLUDE_O) row++;
buffer.append(separator).append(letter(col)).append(letter(row));
if (digits > 0) {
final double precision=MathFunctions.pow10(METRE_PRECISION_DIGITS - digits);
append(buffer.append(separator),(int)((x - cx * GRID_SQUARE_SIZE) / precision),digits);
append(buffer.append(separator),(int)((y - cy * GRID_SQUARE_SIZE) / precision),digits);
}
}
return buffer.toString();
}