This is called for both IFNULL and IFNONNULL instructions.
187356
private void analyzeIfNullBranch(BasicBlock basicBlock, InstructionHandle lastHandle) throws DataflowAnalysisException {

        Location location = new Location(lastHandle, basicBlock);

        IsNullValueFrame frame = invDataflow.getFactAtLocation(location);

        if (!frame.isValid()) {
            // This is probably dead code due to an infeasible exception edge.
            return;
        }

        IsNullValue top = frame.getTopValue();

        // Find the line number.
        int lineNumber = getLineNumber(method, lastHandle);
        if (lineNumber < 0) {
            return;
        }

        if (!(top.isDefinitelyNull() || top.isDefinitelyNotNull())) {
            if (DEBUG) {
                System.out.println("Line " + lineNumber + " undetermined");
            }
            undeterminedBranchSet.set(lineNumber);
            return;
        }

        // Figure out if the branch is always taken
        // or always not taken.
        short opcode = lastHandle.getInstruction().getOpcode();
        boolean definitelySame = top.isDefinitelyNull();
        if (opcode != Const.IFNULL) {
            definitelySame = !definitelySame;
        }

        if (definitelySame) {
            if (DEBUG) {
                System.out.println("Line " + lineNumber + " always same");
            }
            definitelySameBranchSet.set(lineNumber);
        } else {
            if (DEBUG) {
                System.out.println("Line " + lineNumber + " always different");
            }
            definitelyDifferentBranchSet.set(lineNumber);
        }

        RedundantBranch redundantBranch = new RedundantBranch(location, lineNumber, top);

        // Determine which control edge is made infeasible by the redundant
        // comparison
        boolean wantNull = (opcode == Const.IFNULL);
        int infeasibleEdgeType = (wantNull == top.isDefinitelyNull()) ? EdgeTypes.FALL_THROUGH_EDGE : EdgeTypes.IFCMP_EDGE;
        Edge infeasibleEdge = invDataflow.getCFG().getOutgoingEdgeWithType(basicBlock, infeasibleEdgeType);
        redundantBranch.setInfeasibleEdge(infeasibleEdge);

        if (DEBUG) {
            System.out.println("Adding redundant branch: " + redundantBranch);
        }
        redundantBranchList.add(redundantBranch);
    }
549613
private void opNullCheckEndMemST() {
        int mem = code[ip++];   /* mem: null check id */
        int isNull = nullCheckMemSt(mem, s);

        if (isNull != 0) {
            if (Config.DEBUG_MATCH) {
                Config.log.println("NULL_CHECK_END_MEMST: skip  id:" + mem + ", s:" + s);
            }

            if (isNull == -1) {opFail(); return;}
            nullCheckFound();
        }
    }
40630
private boolean equalsNull(String value1, String value2) {
        return (value1 == value2 || value1 == null || (value1 != null && value1.equalsIgnoreCase(value2)));
    }
829362
public static Integer checkNull(Integer value, int elseValue) {
        return checkNull(value, Integer.valueOf(elseValue));
    }
1260001
public static <T> T checkNotNull(T arg, String text) {
        if (arg == null) {
            throw new NullPointerException(text);
        }
        return arg;
    }
232356
@Deprecated
    public static void setTreatNullAsAbsent(boolean treatNullAsAbsent) {
        if (treatNullAsAbsent) {
            configuration = configuration.withOptions(TREATING_NULL_AS_ABSENT);
        } else {
            configuration = configuration.withOptions(configuration.getOptions().without(TREATING_NULL_AS_ABSENT));
        }
    }
213048
private static <T> T firstNotNull(T o1, T o2) {

        if (o1 != null) {
            return o1;
        }
        return o2;
    }
1184634
private final void _writeNull() throws IOException
    {
        if ((_outputTail + 4) >= _outputEnd) {
            _flushBuffer();
        }
        int ptr = _outputTail;
        char[] buf = _outputBuffer;
        buf[ptr] = 'n';
        buf[++ptr] = 'u';
        buf[++ptr] = 'l';
        buf[++ptr] = 'l';
        _outputTail = ptr+1;
    }
746375
@SuppressWarnings("rawtypes")
    private static Object findFirstNonNull(Iterator it) {
        Object result = null;
        while(it.hasNext()) {
            result = it.next();
            if(result != null) {
                break;
            }
        }
        return result;
    }
692670
@CheckReturnValue
  public Joiner useForNull(final String nullText) {
    checkNotNull(nullText);
    return new Joiner(this) {
      @Override CharSequence toString(@Nullable Object part) {
        return (part == null) ? nullText : Joiner.this.toString(part);
      }

      @Override public Joiner useForNull(String nullText) {
        throw new UnsupportedOperationException("already specified useForNull");
      }

      @Override public Joiner skipNulls() {
        throw new UnsupportedOperationException("already specified useForNull");
      }
    };
  }
961400
public void setNull(long mask) {
		for (int i = 0; i < this.numFields; i++, mask >>>= 1) {
			if ((mask & 0x1) != 0) {
				internallySetField(i, null);
			}
		}
	}
401320
void assertNotNull(Object object, String param) {
    if (object == null) {
      throw new IllegalArgumentException(String.format(
          "%s may not be null.", param));
    }
  }
271173
function recursiveCall(i, callback) {
            if(i >= _modules.length) {
                callback();
            } else {
                _modules[i].check(req, res, function () {
                    recursiveCall(++i, callback);
                })
            }
        }
1110208
private void checkForNull(String name, Object value) {
        if(name == null) {
            throw new NullPointerException("name must not be null");
        }
        if(value == null) {
            throw new NullPointerException("value must not be null");
        }
    }
1345755
public static void checkNull(Object o, Object value) {
        if (o != null)
            error(String.valueOf(value));
    }
884376
public static Character checkNull(Character value, char elseValue) {
        return checkNull(value, Character.valueOf(elseValue));
    }
1091417
function () {
            var out = this._curblock.out;
            if (this._curindent) {
                out.push(this._curindent);
            }
            out.push.apply(out, arguments);
            out.push('\n');
        }