Set "potentialNullReference" to "error" level and fixed all issues

There should be no functional change, the logic updated only to make
code simple so that compiler can understand what is going for. Removed
all @SuppressWarnings("null") annotations since they cannot be used if
"org.eclipse.jdt.core.compiler.problem.potentialNullReference" option is
set to the "error" level.

Bug: 470647
Change-Id: Ie93c249fa46e792198d362e531d5cbabaf41fdc4
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit/.settings/org.eclipse.jdt.core.prefs

 org.eclipse.jdt.core.compiler.problem.overridingPackageDefaultMethod=warning
 org.eclipse.jdt.core.compiler.problem.parameterAssignment=ignore
 org.eclipse.jdt.core.compiler.problem.possibleAccidentalBooleanAssignment=error
-org.eclipse.jdt.core.compiler.problem.potentialNullReference=warning
+org.eclipse.jdt.core.compiler.problem.potentialNullReference=error
 org.eclipse.jdt.core.compiler.problem.potentiallyUnclosedCloseable=ignore
 org.eclipse.jdt.core.compiler.problem.rawTypeReference=ignore
 org.eclipse.jdt.core.compiler.problem.redundantNullAnnotation=warning

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheTree.java

 
 			// The entry is contained in this subtree.
 			//
+			assert(st != null);
 			st.validate(cache, cCnt, cIdx, pathOff + st.nameLength() + 1);
 			cIdx += st.entrySpan;
 			entrySpan += st.entrySpan;

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java

 		return ByteBuffer.wrap(copyBuf, 0, bs);
 	}
 
-	@SuppressWarnings("null")
 	void copyAsIs(PackOutputStream out, DfsObjectToPack src,
 			boolean validate, DfsReader ctx) throws IOException,
 			StoredObjectRepresentationNotAvailableException {
 				c = buf[headerCnt++] & 0xff;
 			} while ((c & 128) != 0);
 			if (validate) {
+				assert(crc1 != null && crc2 != null);
 				crc1.update(buf, 0, headerCnt);
 				crc2.update(buf, 0, headerCnt);
 			}
 		} else if (typeCode == Constants.OBJ_REF_DELTA) {
 			if (validate) {
+				assert(crc1 != null && crc2 != null);
 				crc1.update(buf, 0, headerCnt);
 				crc2.update(buf, 0, headerCnt);
 			}
 
 			readFully(src.offset + headerCnt, buf, 0, 20, ctx);
 			if (validate) {
+				assert(crc1 != null && crc2 != null);
 				crc1.update(buf, 0, 20);
 				crc2.update(buf, 0, 20);
 			}
 			headerCnt += 20;
 		} else if (validate) {
+			assert(crc1 != null && crc2 != null);
 			crc1.update(buf, 0, headerCnt);
 			crc2.update(buf, 0, headerCnt);
 		}
 			quickCopy = ctx.quickCopy(this, dataOffset, dataLength);
 
 			if (validate && idx(ctx).hasCRC32Support()) {
+				assert(crc1 != null);
 				// Index has the CRC32 code cached, validate the object.
 				//
 				expectedCRC = idx(ctx).findCRC32(src);
 							Long.valueOf(src.offset), getPackName()));
 				}
 			} else if (validate) {
+				assert(crc1 != null);
 				// We don't have a CRC32 code in the index, so compute it
 				// now while inflating the raw data to get zlib to tell us
 				// whether or not the data is safe.
 			while (cnt > 0) {
 				final int n = (int) Math.min(cnt, buf.length);
 				readFully(pos, buf, 0, n, ctx);
-				if (validate)
+				if (validate) {
+					assert(crc2 != null);
 					crc2.update(buf, 0, n);
+				}
 				out.write(buf, 0, n);
 				pos += n;
 				cnt -= n;
 			}
-			if (validate && crc2.getValue() != expectedCRC) {
-				throw new CorruptObjectException(MessageFormat.format(
-						JGitText.get().objectAtHasBadZlibStream,
-						Long.valueOf(src.offset), getPackName()));
+			if (validate) {
+				assert(crc2 != null);
+				if (crc2.getValue() != expectedCRC) {
+					throw new CorruptObjectException(MessageFormat.format(
+							JGitText.get().objectAtHasBadZlibStream,
+							Long.valueOf(src.offset), getPackName()));
+				}
 			}
 		}
 	}
 		return buf.position();
 	}
 
-	@SuppressWarnings("null")
 	ObjectLoader load(DfsReader ctx, long pos)
 			throws IOException {
 		try {
 			if (data == null)
 				throw new LargeObjectException();
 
+			assert(delta != null);
 			do {
 				// Cache only the base immediately before desired object.
 				if (cached)

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackFile.java

 		}
 	}
 
-	@SuppressWarnings("null")
 	private void copyAsIs2(PackOutputStream out, LocalObjectToPack src,
 			boolean validate, WindowCursor curs) throws IOException,
 			StoredObjectRepresentationNotAvailableException {
 				c = buf[headerCnt++] & 0xff;
 			} while ((c & 128) != 0);
 			if (validate) {
+				assert(crc1 != null && crc2 != null);
 				crc1.update(buf, 0, headerCnt);
 				crc2.update(buf, 0, headerCnt);
 			}
 		} else if (typeCode == Constants.OBJ_REF_DELTA) {
 			if (validate) {
+				assert(crc1 != null && crc2 != null);
 				crc1.update(buf, 0, headerCnt);
 				crc2.update(buf, 0, headerCnt);
 			}
 
 			readFully(src.offset + headerCnt, buf, 0, 20, curs);
 			if (validate) {
+				assert(crc1 != null && crc2 != null);
 				crc1.update(buf, 0, 20);
 				crc2.update(buf, 0, 20);
 			}
 			headerCnt += 20;
 		} else if (validate) {
+			assert(crc1 != null && crc2 != null);
 			crc1.update(buf, 0, headerCnt);
 			crc2.update(buf, 0, headerCnt);
 		}
 			quickCopy = curs.quickCopy(this, dataOffset, dataLength);
 
 			if (validate && idx().hasCRC32Support()) {
+				assert(crc1 != null);
 				// Index has the CRC32 code cached, validate the object.
 				//
 				expectedCRC = idx().findCRC32(src);
 				if (quickCopy != null) {
 					quickCopy.check(inf, tmp, dataOffset, (int) dataLength);
 				} else {
+					assert(crc1 != null);
 					long pos = dataOffset;
 					long cnt = dataLength;
 					while (cnt > 0) {
 							JGitText.get().shortCompressedStreamAt,
 							Long.valueOf(src.offset)));
 				}
+				assert(crc1 != null);
 				expectedCRC = crc1.getValue();
 			} else {
 				expectedCRC = -1;
 			while (cnt > 0) {
 				final int n = (int) Math.min(cnt, buf.length);
 				readFully(pos, buf, 0, n, curs);
-				if (validate)
+				if (validate) {
+					assert(crc2 != null);
 					crc2.update(buf, 0, n);
+				}
 				out.write(buf, 0, n);
 				pos += n;
 				cnt -= n;
 			}
-			if (validate && crc2.getValue() != expectedCRC) {
-				throw new CorruptObjectException(MessageFormat.format(
-						JGitText.get().objectAtHasBadZlibStream,
-						Long.valueOf(src.offset), getPackFile()));
+			if (validate) {
+				assert(crc2 != null);
+				if (crc2.getValue() != expectedCRC) {
+					throw new CorruptObjectException(MessageFormat.format(
+							JGitText.get().objectAtHasBadZlibStream,
+							Long.valueOf(src.offset), getPackFile()));
+				}
 			}
 		}
 	}
 					, getPackFile()));
 	}
 
-	@SuppressWarnings("null")
 	ObjectLoader load(final WindowCursor curs, long pos)
 			throws IOException, LargeObjectException {
 		try {
 			if (data == null)
 				throw new IOException(JGitText.get().inMemoryBufferLimitExceeded);
 
+			assert(delta != null);
 			do {
 				// Cache only the base immediately before desired object.
 				if (cached)

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectory.java

 		return n;
 	}
 
-	@SuppressWarnings("null")
 	private LooseRef scanRef(LooseRef ref, String name) throws IOException {
 		final File path = fileFor(name);
 		FileSnapshot currentSnapshot = null;
 			final String target = RawParseUtils.decode(buf, 5, n);
 			if (ref != null && ref.isSymbolic()
 					&& ref.getTarget().getName().equals(target)) {
+				assert(currentSnapshot != null);
 				currentSnapshot.setClean(otherSnapshot);
 				return ref;
 			}
 			id = ObjectId.fromString(buf, 0);
 			if (ref != null && !ref.isSymbolic()
 					&& ref.getTarget().getObjectId().equals(id)) {
+				assert(currentSnapshot != null);
 				currentSnapshot.setClean(otherSnapshot);
 				return ref;
 			}