diff --git a/src/fsfw/tmtcpacket/pus/tc/PusTcCreator.h b/src/fsfw/tmtcpacket/pus/tc/PusTcCreator.h
index 63a5d45f..3a51fb68 100644
--- a/src/fsfw/tmtcpacket/pus/tc/PusTcCreator.h
+++ b/src/fsfw/tmtcpacket/pus/tc/PusTcCreator.h
@@ -19,6 +19,12 @@ struct PusTcParams {
   uint8_t pusVersion = ecss::PusVersion::PUS_C;
 };
 
+/**
+ * This class provides a high-level interface to create PUS TC packets and then @serialize
+ * them into a raw byte format. It implements @SerializeIF for that purpose.
+ * A custom time stamper can be set, with the implementation of @TimeStamperIF as the only
+ * requirement.
+ */
 class PusTcCreator : public PusTcIF, public SerializeIF, public CustomUserDataIF {
  public:
   PusTcCreator(SpacePacketParams initSpParams, PusTcParams initPusParams);
diff --git a/src/fsfw/tmtcpacket/pus/tm/PusTmCreator.h b/src/fsfw/tmtcpacket/pus/tm/PusTmCreator.h
index a7905858..9f3dcd24 100644
--- a/src/fsfw/tmtcpacket/pus/tm/PusTmCreator.h
+++ b/src/fsfw/tmtcpacket/pus/tm/PusTmCreator.h
@@ -39,8 +39,18 @@ struct PusTmParams {
 
 class TimeStamperIF;
 
+/**
+ * This class provides a high-level interface to create PUS TM packets and then @serialize
+ * them into a raw byte format. It implements @SerializeIF for that purpose.
+ * A custom time stamper can be set, with the implementation of @TimeStamperIF as the only
+ * requirement.
+ */
 class PusTmCreator : public SerializeIF, public PusTmIF, public CustomUserDataIF {
  public:
+  /**
+   * Empty creator with all-default parameters. Please note that serializing this will
+   * generate an invalid PUS packet with no timestamp.
+   */
   PusTmCreator();
   PusTmCreator(SpacePacketParams initSpParams, PusTmParams initPusParams);
   ~PusTmCreator() override = default;
diff --git a/src/fsfw/tmtcpacket/pus/tm/PusTmReader.cpp b/src/fsfw/tmtcpacket/pus/tm/PusTmReader.cpp
index ca40562b..75abdbf6 100644
--- a/src/fsfw/tmtcpacket/pus/tm/PusTmReader.cpp
+++ b/src/fsfw/tmtcpacket/pus/tm/PusTmReader.cpp
@@ -86,6 +86,6 @@ ReturnValue_t PusTmReader::parseData(bool crcCheck) {
   }
   return HasReturnvaluesIF::RETURN_OK;
 }
-bool PusTmReader::isNull() const { return spReader.isNull(); }
+bool PusTmReader::isNull() const { return spReader.isNull() or pointers.secHeaderStart == nullptr; }
 
 PusTmReader::operator bool() const { return not isNull(); }
diff --git a/src/fsfw/tmtcpacket/pus/tm/PusTmReader.h b/src/fsfw/tmtcpacket/pus/tm/PusTmReader.h
index c95fefae..c12bb4c8 100644
--- a/src/fsfw/tmtcpacket/pus/tm/PusTmReader.h
+++ b/src/fsfw/tmtcpacket/pus/tm/PusTmReader.h
@@ -8,6 +8,18 @@
 #include "fsfw/tmtcpacket/pus/RawUserDataReaderIF.h"
 #include "fsfw/tmtcpacket/pus/tm/PusTmIF.h"
 
+/**
+ * This object can be used to read existing PUS TM packets in raw byte format.
+ * It is a zero-copy object, so reading a TM packet with will not copy anything.
+ *
+ * Please note that a parser function must be called after the constructor. This will also check
+ * the packet for validity.
+ *
+ * There are two parser function, where one does not perform the CRC check. This is useful
+ * if the CRC calculation will is performed in a separate step.
+ * This object also requires an explicit time stamp reader to allow flexibility in the used
+ * timestamp.
+ */
 class PusTmReader : public PusTmIF,
                     public RawUserDataReaderIF,
                     public ReadablePacketIF,
@@ -17,11 +29,30 @@ class PusTmReader : public PusTmIF,
   PusTmReader(const uint8_t* data, size_t size);
   PusTmReader(TimeReaderIF* timeReader, const uint8_t* data, size_t size);
 
+  /**
+   * No CRC check will be performed
+   * @return
+   */
   ReturnValue_t parseDataWithoutCrcCheck();
+  /**
+   * Performs a CRC check on the data as well
+   * @return
+   *   - HasReturnvaluesIF::RETURN_OK: Successfully parsed the packet
+   *   - SerializeIF::STREAM_TOO_SHORT: Stream too short for detected packet size
+   *   - PusIF::INVALID_CRC_16 on invalid CRC
+   */
   ReturnValue_t parseDataWithCrcCheck();
   [[nodiscard]] const uint8_t* getFullData() const override;
 
+  /**
+   * Returns @isNull
+   * @return
+   */
   explicit operator bool() const;
+  /**
+   * No (valid) data was set yet or the parse function was not called yet.
+   * @return
+   */
   [[nodiscard]] bool isNull() const;
   void setTimeReader(TimeReaderIF* timeReader);
   TimeReaderIF* getTimeReader();
diff --git a/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.cpp b/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.cpp
index 6ca78378..6a9f6235 100644
--- a/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.cpp
+++ b/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.cpp
@@ -6,12 +6,18 @@ PusTmZeroCopyWriter::PusTmZeroCopyWriter(TimeReaderIF& timeReader, uint8_t* data
     : PusTmReader(&timeReader, data, size) {}
 
 void PusTmZeroCopyWriter::setSequenceCount(uint16_t seqCount) {
+  if (isNull()) {
+    return;
+  }
   auto* spHeader =
       reinterpret_cast<ccsds::PrimaryHeader*>(const_cast<uint8_t*>((pointers.spHeaderStart)));
   ccsds::setSequenceCount(*spHeader, seqCount);
 }
 
 void PusTmZeroCopyWriter::updateErrorControl() {
+  if (isNull()) {
+    return;
+  }
   auto* crcStart = const_cast<uint8_t*>((pointers.crcStart));
   uint16_t crc16 =
       CRC::crc16ccitt(PusTmReader::getFullData(), getFullPacketLen() - sizeof(ecss::PusChecksumT));
diff --git a/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.h b/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.h
index 331bda7f..36c43f51 100644
--- a/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.h
+++ b/src/fsfw/tmtcpacket/pus/tm/PusTmZcWriter.h
@@ -2,6 +2,13 @@
 #define FSFW_EXAMPLE_HOSTED_PUSTMZCWRITER_H
 
 #include "PusTmReader.h"
+
+/**
+ * This packet allows to update specific fields of a PUS TM packet where it is useful or necessary
+ * to update them in a second step. Otherwise, it offers the same interface as @PusTmReader.
+ *
+ * Right now, this class supports updating the CCSDS Sequence Count and the Error Control.
+ */
 class PusTmZeroCopyWriter : public PusTmReader {
  public:
   PusTmZeroCopyWriter(TimeReaderIF& timeReader, uint8_t* data, size_t size);
diff --git a/unittests/tmtcpacket/testZcTmWriter.cpp b/unittests/tmtcpacket/testZcTmWriter.cpp
index c26b0069..fc013590 100644
--- a/unittests/tmtcpacket/testZcTmWriter.cpp
+++ b/unittests/tmtcpacket/testZcTmWriter.cpp
@@ -1,5 +1,6 @@
 #include <catch2/catch_test_macros.hpp>
 
+#include "fsfw/globalfunctions/CRC.h"
 #include "fsfw/tmtcpacket/pus/tm.h"
 #include "fsfw/tmtcpacket/pus/tm/PusTmZcWriter.h"
 #include "mocks/CdsShortTimestamperMock.h"
@@ -16,8 +17,26 @@ TEST_CASE("TM ZC Helper", "[tm-zc-helper]") {
   uint8_t* dataPtr = buf.data();
   size_t serLen = 0;
 
+  SECTION("No Crash For Uninitialized Object") {
+    REQUIRE(creator.serialize(dataPtr, serLen, buf.size()) == result::OK);
+    PusTmZeroCopyWriter writer(timeStamper, dataPtr, serLen);
+    REQUIRE(writer.getSequenceCount() == 22);
+    writer.setSequenceCount(23);
+    // Can't set anything, parse function was not called
+    REQUIRE(writer.getSequenceCount() == 22);
+    writer.updateErrorControl();
+  }
+
   SECTION("Basic") {
     REQUIRE(creator.serialize(dataPtr, serLen, buf.size()) == result::OK);
-    PusTmZeroCopyWriter(timeStamper, dataPtr, serLen);
+    PusTmZeroCopyWriter writer(timeStamper, dataPtr, serLen);
+    REQUIRE(writer.parseDataWithoutCrcCheck() == result::OK);
+    REQUIRE(writer.getSequenceCount() == 22);
+    writer.setSequenceCount(23);
+    REQUIRE(writer.getSequenceCount() == 23);
+    // CRC is invalid now
+    REQUIRE(CRC::crc16ccitt(dataPtr, serLen) != 0);
+    writer.updateErrorControl();
+    REQUIRE(CRC::crc16ccitt(dataPtr, serLen) == 0);
   }
 }
\ No newline at end of file