It is triggered in the unit test FindhasZeroByte at line 705, and in some of the following calls:
Alexanders-MacBook-Air:Debug alexanderstigsen$ valgrind --track-origins=yes ./tightdb_unit_tests
==88587== Memcheck, a memory error detector
==88587== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==88587== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==88587== Command: ./tightdb_unit_tests
==88587==
==88587== Conditional jump or move depends on uninitialised value(s)
==88587== at 0x1000DCE09: Array::FindNaive(long long, unsigned long, unsigned long) const (Array.cpp:608)
==88587== by 0x1000DCBEC: Array::Find(long long, unsigned long, unsigned long) const (Array.cpp:535)
==88587== by 0x100019431: hasZeroByte(long long, unsigned long) (testarray.cpp:687)
==88587== by 0x100019895: TestFindhasZeroByte::RunImpl() const (testarray.cpp:705)
==88587== by 0x1000D542D: void UnitTest::ExecuteTest<UnitTest::Test>(UnitTest::Test&, UnitTest::TestDetails const&) (ExecuteTest.h:25)
==88587== by 0x1000D4E7B: UnitTest::Test::Run() (Test.cpp:34)
==88587== by 0x1000D6016: UnitTest::TestRunner::RunTest(UnitTest::TestResults*, UnitTest::Test*, int) const (TestRunner.cpp:61)
==88587== by 0x1000D69B7: int UnitTest::TestRunner::RunTestsIf<UnitTest::True>(UnitTest::TestList const&, char const*, UnitTest::True const&, int) const (TestRunner.h:40)
==88587== by 0x1000D5EC8: UnitTest::RunAllTests() (TestRunner.cpp:17)
==88587== by 0x100084263: main (main.cpp:4)
==88587== Uninitialised value was created by a heap allocation
==88587== at 0xD6D9: malloc (vg_replace_malloc.c:266)
==88587== by 0x1000D9CC7: Allocator::Alloc(unsigned long) (alloc.h:21)
==88587== by 0x1000DA34E: Array::Alloc(unsigned long, unsigned long) (Array.cpp:1191)
==88587== by 0x1000DA192: Array::Array(ColumnDef, Array*, unsigned long, Allocator&) (Array.cpp:27)
==88587== by 0x1000DA0B2: Array::Array(ColumnDef, Array*, unsigned long, Allocator&) (Array.cpp:23)
==88587== by 0x100019352: hasZeroByte(long long, unsigned long) (Array.h:69)
==88587== by 0x100019895: TestFindhasZeroByte::RunImpl() const (testarray.cpp:705)
==88587== by 0x1000D542D: void UnitTest::ExecuteTest<UnitTest::Test>(UnitTest::Test&, UnitTest::TestDetails const&) (ExecuteTest.h:25)
==88587== by 0x1000D4E7B: UnitTest::Test::Run() (Test.cpp:34)
==88587== by 0x1000D6016: UnitTest::TestRunner::RunTest(UnitTest::TestResults*, UnitTest::Test*, int) const (TestRunner.cpp:61)
==88587== by 0x1000D69B7: int UnitTest::TestRunner::RunTestsIf<UnitTest::True>(UnitTest::TestList const&, char const*, UnitTest::True const&, int) const (TestRunner.h:40)
==88587== by 0x1000D5EC8: UnitTest::RunAllTests() (TestRunner.cpp:17)
==88587==