Here's what I'd try for this for loop:

                for (; i < children.size(); i++) {
                    // This logic finds the common type to which all child types are coercible
                    // without losing precision.
                    PDataType type = children.get(i).getDataType();
                    if (type == null) {
                        continue;
                    } else if (type.isCoercibleTo(PDataType.LONG)) {
                        if (theType == null) {
                            theType = PDataType.LONG;
                        }
                    } else if (type == PDataType.DECIMAL) {
                        // Coerce return type to DECIMAL from LONG or DOUBLE if DECIMAL child found,
                        // unless we're doing date arithmetic.
                        if (theType == null
                                || !theType.isCoercibleTo(PDataType.DATE)) {
                            theType = PDataType.DECIMAL;
                        }
                    } else if (type.isCoercibleTo(PDataType.DOUBLE)) {
                        // Coerce return type to DOUBLE from LONG if DOUBLE child found,
                        // unless we're doing date arithmetic or we've found another child of type DECIMAL
                        if (theType == null
                                || (theType != PDataType.DECIMAL && !theType.isCoercibleTo(PDataType.DATE) )) {
                            theType = PDataType.DOUBLE;
                        }
                    } else {
                        throw new TypeMismatchException(type, node.toString());
                    }
                }